In Top Gun II, Maverick is still a Captain after 25 years in the Navy!
The answer is that Scientology has made him quarrelsome, argumentative, and an antisocial personality. Maverick constantly attacks Psychiatry. Everyone one on the ship is sick and tired of hearing his same goddamned opinions over and over after 20 years. “Put a sock in it Maverick!” ordered Rear Admiral Braisted.
Maverick is also hiding secrets: How does the aging OT jet jockey keep the flight surgeon from finding out he has a very bad case of hemorrhoids? And how does the fading Top Gun pay alimony to three ex-wives on a US Navy salary?