Data is probably the one character they could have built another show around, either a prequel or sequel.
For a mundane answer, I would suggest Star Fleet simply loaded him up with work, 24/7 with not even lodgings of his own, and he had no "off time" analogous to human sleep to process non- work related matters, stunting his growth as a person.
Afterall, timewise, he's someone that can put in the hours of 4-5 people, and is at least 4x as efficient as each person. So we're talking about someone who can do the work of 20 people, and that would be hard to not take advantage of. And it might have started innocently enough, with Data subbing for a crewmember on leave on top of normal duties. The promotions may not even been for his benefit and merely give him appropriate access for his tasks, and until his trial, Pocard could have chosen to ignore his rank or summarily lowered it without cause if he wished.
So the previous crews just had less time away from a professional capacity to interact with him and he had less to personal stuff to process. This would make sense with his early appearances as he was quite comfortable with professional conduct but a child once it came to other things.
i would suggest in the academy he was more of an outcast than later on, because teens and young adults can be most like that, especially after the novelty factor wore off and Data coming across as he does.