In a recent interview, Kosuke Yabuki, the producer of Mario Kart World, shed light on the decision to exclude crossover characters from other Nintendo franchises. He emphasized that the development team felt it would be incongruous to introduce characters from different universes into a game that is fundamentally centered around the Super Mario world. This choice reflects a commitment to maintaining the integrity of the Mario brand while ensuring that players can still enjoy a diverse cast of characters from within the Mario universe.