The studios of Disney's affiliates seem to have a penchant for breaking with tradition, because only a few months after Avengers: End of the game prompted viewers to sit in the credits just to hear Tony Stark's ghost hitting metal in place of a traditional stinger, Toy Story 4 will open in theaters without too long to test everyone's patience before the character himself is created. This will Toy Story 4 the first Pixar movie since the original Toy Story not to be associated with a short film of theatrical animation, with 1998 The life of an insect launch the tradition with the winner of an Oscar Geri's game.
This comes from Slate, which indicates that Pixar's new SparkShorts program allows the studio to create new short films that are separate from movie films. So it is possible that the studio realizes that there is now a better way to do these things. Or, considering that the shorts were either really good (it's probably fun to collect Oscar nominations), or really terrible, maybe Pixar decided that he did not like it no longer play that game. OrTo propose a third theory, Pixar may be lacking the means to create a cute cartoon that is also really sad.