Not everyone ages the same way ...some people age well others not.
Who is to say that she should heave keep the weight off?
she can gain 100 more pounds as far as I care but she was in Top Gun because of her looks not her acting ability.. that said she also wasn’t a vital part of the movie(the minor role as a love interest} and certainly her part wasn’t needed for the sequel just like Pussy Galore wasn’t in later Bond films.. time moves on.. the film is about Tom Cruise’s character and airplanes..
I pretty sure nobody including viewers, Cruise and the movie producers want to see his ex 62 year old 250lb girlfriend with a butch haircut come strolling in...IMHO