The bottom line on the ratings is that TNG is the only Trek series to ever be a consistent success in its initial run with a general viewing audience. Something about it connected with the viewing public in a way that the other shows did not. I think today we often forget how successful TNG was and how much of a gulf there was overall between the shows. TNG was regularly pulling numbers that rivaled Monday Night Football.
Personally, I think Paramount made a big mistake shifting TNG to the big screen. First Contact was its only real big success in that venue, and none of the other shows were able to duplicate its ratings on the small screen. The folks at Paramount seemed to think that because TNG was a hit, anything with "Star Trek" attached to it would automatically be a hit as well. If nothing else, TFF should have shown them that was not the case.
I also agree that the TNG films were a mistake. But the TOS crew were done with making movies, and Paramount wanted their Kirk-meets-Picard story to springboard the big-screen cash cows that Shatner, Nimoy and Kelley were no longer providing. Then it just became the Picard & Data show.
AGT was the perfect ending to TNG. If I never saw those characters again, I would have been happy with that.