To open up Animation Courtyard for a larger property (it could definitely receive one down the road)
Disney has kinda been clear that they want to keep expansion plots open when they can and will choose a more complicated process to do so (See ROA)
Do I think they necessarily WILL bring Muppets over? Not 100% but with the pushback I could imagine them considering it. If I was Disney, I would consider putting Muppets in a renovated Lightning Mcqueen Racing Academy Theater, retheme RocknRollercoaster to Mayhem, and make a Muppets Miniland over by RnRC, put Monsters where MV is right now, and put something like Avengers Campus (not possible rn) or Zootopia in Animation Courtyard to better use up all of that large amount of space.