Which Undiscovered Country essentially did. They were rounded up from one more mission while they were mostly doing their own thing, like Uhura hosting a seminar at the Academy, and Sulu already having left for the Excelsior.The issue was that at the time, Paramount's plan was to have both the new Enterprise-D crew have the TV adventures on TNG, and the old crew were to have adventures in the films, concurrently, on the Enterprise-A. The inherent problem with this scenario, however, was that the old crew were past their prime for this, not to mention that the TNG crew started to overshadow them (which Shatner, Nimoy and the rest did not expect to have happen.) It would have been different had the future films dealt with the old crew going their separate ways, but TFF blew that idea out of the water by essentially putting the entire cast right back to where they were in TOS. It was unrealistic, it ultimately didn't work, and a final film had to be made to pretty much address this inherent problem.
What I feel should have happened though is, The Next Generation should have still been in the 23rd Century, running alongside the films, allowing for crossover between them. The occasional cameo like how we saw McCoy, Spock, and Scotty, but also potential cameos from the show into the movies. Now it wouldn't have been the Enterprise-D of course, as it should have been the Excelsior being the new hero crew of the TV series. Come Star Trek VI, Sulu would simply have to get a different ship... and y'know what? Have Picard and his crew on the Excelsior saving Kirk and crew at Khitomer. That would have been the PERFECT crossover moment and final farewell to the TOS cast.
And this would have prevented the issue where technology progressed so slowly between the 23rd and 24th centuries. If they were at the same time, seeing the TNG sets in Undiscovered Country would no longer have been odd.