Majority of the TOS movies were made with the belief that each film would be the last one. I believe Leonard Nimoy said something to that extent in one of the dvd interviews on the movies. The TOS films put alot of thought into making their movies as entertaining as they could with what they were given.
If you look at the TNG movies, they seem to be made with the premise that they'll always have another one to do. While it wasn't totally unfeasible for TNG to make more than 4 movies. Berman put all his eggs in the VOY basket. VOY being billed as the "next TNG". Recent interviews with Marina Sirits, Levar Burton, Johnathan Frakes, Brent Spiner and Rick Berman they all say that Paramount wanted the TNG films to end at Insurrection an wasn't interested in another TNG film. Berman was able to talk them into making Nemesis but the fan base wasn't paying attention and it didn't make a profit at the BO. Had Nemesis been successful we would've had a 5th TNG film. DS9 was fantastic but didn't make as big a return as Paramount wanted. VOY copied as much of TNG as they could but was still hemorrhaging ratings. The franchise was stalling. If Berman hadn't set up DS9 and VOY to compete alongside the film series, the TNG movies could've been better.