Continuing to give these characters satisfying endings, just to undo them again in a sequel, will eventually cause audiences to lose trust in these big emotional moments in the Toy Story franchise, and the impact will be significantly lessened.
The goodbye between Woody and Buzz at the end of Toy Story 4 held the emotional weight of the movie, which is why the idea of bringing them back together so soon in Toy Story 5 has already led some to criticize Pixar's decision for another sequel.