Ttyjukl

In short, taking the Bridge Officer's test doesn't confer instant rank. That's still the gift of the Captain, with the approval of Starfleet Command.

Troi (who already holds the rank of Lieutenant Commander because of her medical qualification) is able to become an Officer of the Deck (OOD) as a result of her having taken the test and is then given an enhanced rank as a recognition of her enhanced responsibilities and long service. It seems that Troi has been told that what's blocking her from rank is that she isn't qualified to be OOD.

LaForge and Data have likely already passed the Bridge Officer's test (since Data is Second Officer and in charge of the night shift and we see LaForge in command on several occasions). They would presumably have to wait for promotion as a result of longer service or recognition of their duties in other ways.

Out of Universe, the show's producer Jeri Taylor responded to this exact question:

I thought it was really strong, although we have taken some criticism from people who said, 'How could you promote her over Data and
Geordi?' But it would not have been a very interesting story to see
Geordi or Data getting their rank. The obstacles she had to overcome
were formidable and where you get interesting drama is out of
conflict"

This is one of the more clear cut examples of a flaw in the TNG script, and is akin to 'The Wesley Problem'. From a Universe perspective, an officer's rank and the command structure of a ship are two separate (but often similar) things. Each position (2nd in command, third in command, Chief Engineer etc) has a recommended rank for the role, but officers can be promoted above (and actually be below)this rank if the situation allows for it - Troi was a commander, yes, but somewhat ceremoniously as her command status on the ship remained unchained since her role/qualifications were outside of/unsuitable for the main leadership structure. She had a high enough rank to take a shot at that promotion due to her medical qualifications. Since Data, Geordie etc were central to the command structure, my guess is that if they were to achieve promotion it would have to be due to merit that showed they could fill a direct advancement up the tree, rather than no one leaving and that character being promoted to the same rank as a technically, more senior officer, as this may cause awkward respect/discipline issues between those two officers and the crew under them. Since Riker (nor the other characters for that matter) wasn't going anywhere, Data couldn't advance to take his place, and so neither could Geordie etc.

However, from a writer's perspective, my suspicion is that the reason they promoted Troi was that 1) They needed to give her character something to do - an arc of personal growth over the later seasons 2) Moreover, they needed to boost her sense of qualification in the audience's mind - being empathic made her the perfect person on the ship to be the Captain's aid, so that's a reason why she should be on the bridge/by Picard's side, but other than that there was little reason for many people for her to be a senior officer, and have some form of command presence over others, when she wasn't qualified to do so. The real reason she had all that screen time of course was cause she was an important character not officer. This is 'The Wesley Problem' - it annoyed a lot of people that you had a character in the middle of scenarios they ordinarily wouldn't be in, just so stories could be written about them.

Riker actually briefly mentions the other parts of the test in the episode, which include the abilities to handle Diplomacy and First Contact. I can definitely see how Data might have problems with Diplomacy with his inability to fully relate to emotions. With La Forge, he was promoted to Lt. Commander during the series, so he might need more experience in that rank

In the real world military as I understand it, rank is dependent on job. If your job is to command forty people, that's one rank. Four hundred is a higher rank, because otherwise you couldn't have a hierarchical structure. So Data and LaForge don't get promoted because their rank is appropriate to their function, and their functions don't change. (Past season two, at least, where we see LaForge get both a new job and a promotion.) Troi gets a new function which requires her to be able to give orders to others of equal rank and greater experience. Giving her a higher rank helps overcome the experience deficiency from a hierarchical standpoint.

Now why Worf got promoted, I have no idea.

Medical officers are ranked up faster to start with because of the education and training they have to go through even in real life military, Bashir is a good example he was on his first assignment and was already a lieutenant(jr grade). Troi had massive amounts of field experience which usually counts for a lot in military/sciences and had emergency command experience by that point(the whole reason she took the test)...data and the others started out at a lower rank on there first assignments (ensign), Troi was possibly like Bashir an ensign while still at the Acadamy getting her degrees, this means they ranked up slow based on merit alone while she ranked faster based on her academic career and once assigned off of merit alone, in other words she had most likely not been ranked sense she left starfleet while data and geordie had no rank up tell after they left starfleet(also remember they both ranked from Lt.(full) to lt. commander at some point after season 2. now explaining how Tom and Tuvok ranked up and lost rank at least once each, while Kim never even ranked even though hes acting chief of operations thats super strange.

As a rule, there are posts and there are ratings. "Captain" can refer to a post on a vessel, or a pay grade (rank or rating) of an individual. Your rank is determined by the number of people that your superiors trust you o immediately command. You can be a Lt. CDR in rank, and still be captain (skipper) of a vessel with a crew of 100, as on a submarine. A vessel the size of Enterprise, with a crew of over 1,000, would be more along the lines of skippering an aircraft carrier. Anyone permitted to take a command shift would have to be of a higher officer rank, regardless of posting or MOS. Pretty much all Star Trek, with the exception of Nicholas Meyer (Wrath of Khan, Undiscovered Country), has played the command structure hierarchy rather loosely, because Trek is an ensemble drama. In an actual reality based hierarchy, Picard and Riker would've either been promoted or forced into retirement somewhere around season 5, and the whole cast would've been given new assignments and promotions throughout the show, especially in light of their numerous successes.