Data appeared to be happy serving aboard the Enterprise-D, learning & growing there, serving as the Operations Officer. Perhaps he could've earned the rank of full commander, but didn't, presumably until Riker accepted promotion to captain of the Titan, thereby Data was promoted to First Officer of the Enterprise-E.
The character of Data was created to mirror the human condition, so if you promote the character, perhaps have him serving away from the Enterprise, you only have Worf for a mirror. Then you might want to create another character to replace Data.
Once TNG became successful, why promote the character (again perhaps away from Enterprise) if the actor is happy in their job? If Brent Spinrer had wanted to leave, than perhaps promotion had worked as a way to leave.