Ttyjukl

Not too sure about an in-universe explanation, but Star Wars concept artist Iain McCaig in Art of Star Wars: The Force Awakens presented some ideas that played around with the concept of what Anakin’s “Force Ghost” was meant to represent in The Force Awakens:

‘When you light a candle, you also cast a shadow.’ That inspired me to
propose, for the first time, that Anakin’s ghost could come back […]
If we see Anakin Skywalker, because he does flow back and forth
between Darth Vader and Anakin, let’s see him as a character with a
dark and light side. The reason Luke is this whole new entity is
because he was the first to acknowledge his own dark side — that it
was not separate from him.

The ideas were ultimately discarded, but to me it shows that somehow the idea of Anakin appearing to Kylo as some kind of “Force Ghost” adviser was tossed around. Looking at the concept art one can assume that the idea would be that even in the afterlife Anakin is conflicted with the light and dark side of himself. Which might actually explain Kylo’s conflict as well; if Anakin was not 100% good or evil, then who is to say what really destroyed him?

But the more you think about this, the more mucked up and confusing it becomes since the whole concept of Anakin being “young” as a “Force Ghost” in the reworked ending of Return of the Jedi was meant to convey he was “good” when he was that age… So then if he’s conflicted shouldn’t half his face be the old Anakin (aka: Sebastian Shaw)? And then what does that mean even from a visual standpoint?

Better just show the burnt mask and then explain some kind of… I don’t know… Some crazy necklace or bracelet Kylo wears that blocks any “good” things from reaching him. You can market anti-“Light” baubles easier than some “two-face” mask right?

The passage from the Thrawn Trilogy novels (now considered Legends canon) where Obi-Wan's Force Ghost bids farewell to Luke Skywalker implies it requires some effort by a deceased Force user to sustain themselves as a separate spirit, and that eventually they merge with the Force.

In addition, I thought it was stated in Legends canon that Obi-Wan and Yoda had mastered the trick of preserving their spirit as a Force Ghost, while Anakin had not (although some Sith were capable of existing as Force Ghosts).

I think there are multiple reasons why Anakin's force ghost did not appear to Kylo Ren throughout The Force Awakens:

1. Disney wanted to reboot the franchise and did not want to mention anything from the prequels

This does not mean that the prequels aren't canon--they are. But Disney did not want to mention them due to them being hated by the majority of the Star Wars fandom. Several materials teasing a romance between Shmi Skywalker and Qui-Gon Jinn as well as the mention of midi-clorians were scraped due to Disney not wanting to upset fans. This is probably why any concepts involving Anakin Skywalker's ghost was eventually given up on. And if followed, Hayden Christensen would have had to reprise his role as Anakin which probably would have been refused by the actor who received backlash for his acting in the prequels.

2. Kylo Ren idolizes Darth Vader

Kylo Ren views Anakin as being weak and foolish, he would not listen to his ghost even if he appeared. Han Solo stepped into the role of advisor, rather than Anakin, to try to speak to Ren's conscience. Kylo Ren talks to Vader, not Anakin. Vader could not appear before Kylo since he was killed by Anakin upon saving his son. If Kylo killed Han after his pleas to come home, it is safe to assume that he would have paid no heed to his grandfather's ghost.

3. It does take effort to appear as a Force ghost

This is addressed in the canon Star Wars book, Beware the Power of the Dark Side! (by Tom Angleberger):

P163

Like most Jedi, Obi-Wan became part of the Force when he died. But Obi-Wan did something the others did not. Guided by the discoveries of his own master, Qui-Gon Jinn, Kenobi found a way to live after death and even return to walk briefly among the living. Not for himself, not for some greedy dream of immortality, but to continue the great fight against evil and tryanny. It takes great effort, a great will, but he collects himself, pulls together the pieces of his consciousness from the endless flowing energy of the Force, and appears before Luke. He cannot do this often, only at key moments in Luke's journey, when a misstep might spell doom, not only for Luke, but for any hope of bringing balance back to the Force and freedom to the people of the galaxy.

P170

Obi-Wan can sense his strength growing weak. He cannot bend the laws of nature any further. He must go.

4. Han Solo said everything that could be said to Kylo

As I said before, Han Solo stepped into the role of advisor and in place of Anakin's force ghost. If Anakin's ghost appeared, there would not be as much of an emotional stake as we have not had any interaction with the two of them. By keeping Anakin out of the way, there is more of an emotional tie to the character to know how he would view his grandson's actions. But it also creates an emotional bond to the character of Han Solo, his development as a character, and his relationship with his son. Han said everything that needed to be said: how much Ren was still loved by his parents, they were willing to forgive, Snoke's true intentions, and that there was still good in him. It reminds the audience of Han's heart of gold, raises the stakes, and will form Kylo Ren's path to the light or the darkness.
It also bonds the audience to Anakin Skywalker, not Darth Vader, to know how the character would view his grandson's actions.

I would like to be proven wrong on this but I suspect the following.

There are explicit dark and light side techniques. The ability to produce a Force Ghost is explicitly a Light Side technique. The ability to communicate with Force Ghosts may also be a Light Side technique. Whether or not Kylo Ren is capable of it, he may not be willing to perform a Light Side technique to be swayed by a Skywalker.

People need to remember Anakin's ghost, old or young Prouse or Christenson, appears to Luke to narratively confirm that Luke has succeeded in redeeming his father, Anakin. It's more about the story's needs than being consistent about how the Force works.

All this talk of Darth Vader and Anakin as "different people" is merely taking semantics as reality; they were NOT two people, they were one person who desperately (and hopelessly, possibly even clinically depressed) telling himself that his old life is over and his new self is all that is left.

Remember, he killed every person he ever loved or cared about only to learn that it was all for nothing. He was consumed with self-loathing, hatred of everyone except possibly his master [in some comics, he seems to actually love or revere his master, which is either a brilliant way to show that some part of Anakin's old self is within him, or just made for a better story], and the pathetic need to make everyone around him submit or suffer as he was suffering.

He's a deeply pathological personality after his fight against Obi-Wan. I think people are making a mistake being too literal about the Sith Lords' habit of taking a new name. The Dark Side twists you into a new form, it doesn't change a person irrevocably; otherwise, redemption would be logically impossible.

Vader no longer exists; he ceased to exist when Anakin's real persona asserted itself. Praying to the ashen ruin of Darth Vader's mask is just a pathetic but brilliant way of showing how obsessive Ren is about his hero; he's a pathological fan-boy with major daddy issues.

IMHO, he's way too much mentally ill to be very sympathetic. As others pointed out, Ren is in full possession of all the facts about the Dark Side and what his grandfather did; how you then decide killing your friends, destroying everything your uncle is trying to do for the galaxy, betraying your mother and ultimately murdering your father just to prove to yourself that you're committed to an illogical and self-destructive support of the most evil regime in galactic history ... even if Anakin had received the training Yoda and Obi-wan had, would you want to talk to this little snot?

As a post-script:

They better give one hell of a good reason for why Ben Solo is so full of hatred and resentment and neediness in the next film. Having famous and probably inattentive parents, one of whom is probably not the galaxy's best dad, just not seem adequate explanation. Anakin was lied to and manipulated by a person who had been doing it and playing on his character flaws for years; he was weak and foolish and power-hungry, but he did think he was saving the person he loved most in the world. Ben Solo had nothing selfless about what he did. He wasn't trying to save anyone. He just wanted power, and to hurt his parents. Sad.

Like has already been said, Kylo Ren idolizes Darth Vader, NOT Anakin Skywalker. Kylo Ren likes the powerful and evil things that Darth Vader did, and considers his pull back to the light side a weakness. In Kylo Ren's chambers, he apologizes to Darth Vader for feeling a pull to the light side again. He obviously thinks that Anakin was weak for choosing the light side and Darth Vader was strong for being a part of the dark side.

Both men of the Skywalker- Solo clan (Luke and Han) went MIA instead of staying and dealing with Kylo. It would make sense that, after doing what he did as Vader, Anakin also goes into some sort of self banishment out of guilt. If that is the case he likely has no idea that his grandson has fallen to the dark side. This would also explain why Obi-wan tells Rey "these are your first steps" instead of Anakin as 1. it's Anakin's lightsaber and 2. Rey is possibly Anakin's granddaughter.

The reason why Kylo Ren cannot have a " force vision " of Anakin is quite simple. It's quite a sad story after Anakin returned back to the light side of the force after Luke saved him from the dark side Anakin then became one with the force and with that became available only to Luke because of the very strong " Force bond " between father and son and that's why.

I hope this has been helpful.

The Force Ghost is that of a Jedi, one who has crossed to the light of the Good side of the force. Kylo has not crossed to the Light, he has embraced the dark
and in doing so, prevented any Jedi Force Ghost from crossing to him.
It has also been interpreted that when Obi Won was struck down, he was not killed, he was already dead, and came about to help Luke, as was his life's mission.
The same with Yoda, when Luke returned to the plant, it was the return of the Jedi, if you listen to what Yoda says, it eludes to how he can't hang on to the physical anymore.
The metaphysics Lucas used were vague, and most likely intentionally so, so as to provoke thought, and avoid explanations.

That's like asking why Yoda and Obi Wan don't appear as force ghosts at Darth Vader. The story doesn't include good force ghosts tormenting bad Jedis.

Remember when Luke insisted on going to rescue Leai and Solo. Obi Wan said if you do that "I cannot interfer".

It could be that Anakin has tried and Kylo Ren is unable to hear and see him due to him turning to the dark side.