Kingdom Hearts lead Tetsuya Nomura says that Pixar's Coco was chosen as a Disney world in Kingdom Hearts 4 as it was the best fit for Sora's story.
Speaking at the Kingdom Hearts D23 panel (via Genki_JPN on Twitter), after the reveal that The Land of the Dead from Pixar's Coco is the first Disney world featured in the upcoming Square Enix RPG Nomura spoke about world selections.