You could blame DS9 for this. Prior to DS9, Paramount was wary of having two Trek shows on at the same time. Initially, they flat-out told Berman and Piller they would never do a Star Trek spinoff. A year or so later, Paramount asked Berman and Piller to develop ideas for new shows, Star Trek-related or not. One idea they had was Deep Space Nine. Another idea was an SF series set during medievel times. Paramount went ahead with DS9, but still had reservations about having two Treks running simultaniously. They already had a huge success with TNG; you can't really blame them for not wanting to rock the boat.Paramount got greedy, and rushed out Generations and VOY at the same time, as well as TNG season 7. The quality suffered as a result.
DS9's success convinced Paramount they could slap the Star Trek name on anything and it would be a huge hit. They decided then that, once TNG went to movies, they should still keep running two Trek shows.
So you see, it's all DS9's fault for not tanking.
