That is understandable. Because of how Jason helped to jump start the Muppets and to make a good movie, I would imagine that one of his close colleagues would feel more satisfied with Jason's approval.
That and the fact he has a name for himself in Hollywood. Unless you're a big name, they usually don't let you have any freedom in your films. And I really don't think Disney would have done
that movie without his famous name attached to it. I mean, it is the first Muppet Movie to really headline the human actors over the Muppets in the marketing. Even MCC with Michael Cain wasn't marketed as such, and the whole movie was about him. Probably had more screentime than Jason, too.
But Jason's absence is understandable. He probably is working on 5 other movies at the moment,
and he has that show that's about to end. I kinda wanna see him as a cameo, though. But he doesn't need to make the next movie. The Muppets can speak for themselves at this point.