Because some people cant open up to good kino games, they just need to have Zelda slapped onto their titles and people will love them
Jokes aside though, some shortsighted Nintendo fans who only look at the names of their big mainstream titles they support essentially want to see them becoming a boring Call Of Duty support studio like the hundreds of studios under Activision that are trapped forever making Call Of Duty games, when what truly makes a company shine and expand on their talent is to make original IPs and what they want. None of the talent you see growing at Monolith comes from them wanting to support Animal Crossing or Splatoon, it comes from wanting to make Xenoblade.