Stitch resides in Hawaii, Mermaid is Dutch waters, Pinocchio is a German village, and Tinkerbell is British. Yes, they are fictional characters from fictional settings, but there are very strong ties to a specific location.
There is 0 connection of Groot to Earth, let alone any country.
And even if we ignore all that, what diversity do we have? Black Panther in Africa, Thor in Norway (I guess?), and everyone else from the good ol' USA?
It's also not lost on me that adding Marvel Characters kinda goes against the whole principal theme of the ride. Adding War Machine to a ride about holding hands and singing for peace and love is weird AF.
It all just screams "We got the Marvel rights now, let's just throw stuff together and see what sticks."