Mario Kart World has a vast array of playable characters from the Mario universe, but fans were disappointed to see no non-Mario faces, such as Link from The Legend of Zelda or Isabelle from Animal Crossing. Producer Kosuke Yabuki shed light on this decision, stating that other Nintendo characters wouldn’t fit the universe and that Mario alone offered enough possibilities.
According to Yabuki, it would be incongruous to introduce characters from outside games into the Mario Kart World universe. Instead, the development team focused on what they could already do with Mario. The upcoming game features numerous characters and costumes, ensuring there’s something for every player.
Yabuki also laughed off suggestions that ARMS characters were considered for the game, dismissing them as unrelated. This decision marks a departure from previous comments by the development team, which mentioned NPCs like Cow becoming part of the playable roster.
Source: https://nintendoeverything.com/mario-kart-world-nintendo-characters