Pixar had become a part of Disney and standards were falling. Lasseter had to go, and Pixar films were not doing well.
Then suddenly, TS4. It was downhill again, but finished the story with Woody going off with Bo Peep, never to be seen again, and the rest of the characters realising they were friends with a plastic spoon.
It did OK, and drew a thick line under the whole story. Toy Story was done forever.
Until 2026, and now, with Pixar needing a hit and a lack of new ideas, Toy Story 5.