The studio’s desire to make Star Trek VI the last original series movie was, in my opinion a terrible marketing move. Star Trek VI would be the 15th highest grossing film of 1991 and have the best opening weekend of any movie up to that date. Star Trek VI had a worldwide take of around a hundred million dollars from a twenty five million dollar budget. This profit excludes VHS, DVD and now Blu-Ray sales.
Meanwhile TNG was acheiving massive ratings on TV and interviews from the time suggest that none of the cast wanted it to end. Furthermore, when they did make Generations, it was done on the cheap.
No, they made the right call. Even if Paramount could have still afforded Shatner & Co., they would've gotten two more films (at best) out of them before DeForest Kelley would've gotten too sick to go on. And TNG was just about out of gas story-wise by the end of the seventh season - any longer and it would've gotten as bad as Voyager
ended up becoming.
In fact, VOY was a large part of the reason Generations
was done so cheap and why the TNG crew barely got to pause for breath after the series finale before launching into the movie - they had
to tear down the Enterprise-D sets to replace them with the Voyager sets in time for a January '95 premiere.