TNG was an ensemble series on television. On film, it became the Picard/Data show. TOS was about three characters with a supporting cast. That dynamic was maintained, more or less, in the film series (though McCoy doesn't always get as much to do as he did on the series).
TNG probably would have worked better as a series of telemovies, which would have allowed for more time to highlight the ensemble in a way that wasn't possible with four movies made over the course of a decade.
I doubt they would have been able to make even 4 telemovies.
Stewart and Spiner could only be kept because they were starring motion pictures. According to imdb, Stewart got a salary of 15 million for Nemesis, which would mean that he was one of the highest paid motion pictures actors at that time. They couldn't have financed that with a TV film budget.