Though many of Disney’s properties have appeared in Kingdom Hearts games over the years, Star Wars and Marvel were noticeably absent from Kingdom Hearts 3 – and the reason why is, frankly, kind of boring.
Kingdom Hearts 3 Ultimania, the official companion book for the most recent Kingdom Hearts game, includes a special interview with director Tetsuya Nomura. Translated by Twitter user @lunesacree via KH13, Nomura reveals why properties from Marvel and Lucasfilm weren’t included in the game, and it mostly boils down to contract complications – the same reason why Mickey Mouse was barely in the first Kingdom Hearts.
Source: IGN.com The Reason Star Wars and Marvel Aren't in Kingdom Hearts 3 Is Dull