Mickey Mouse is massive. Mickey has been the face of Disney and is sold on and in many products each year. Kids know who he is and adults know who he is. He does seem antiquated now, especially to older adults but I don't see them getting rid of him anytime soon.
Disney doesn't have many characters with that much lasting appeal between age demographics, it links the older generation of Disney with the new.
The version of Mickey Mouse that would become public domain in 2024 bears very little visual similarity to subsequent versions. Still recognizable, but definitely not the same. Only the initial works from that year will be public domain.
You won't be able to recreate Disneyland with this public domain entrance.
Disney doesn't have many characters with that much lasting appeal between age demographics, it links the older generation of Disney with the new.