Honestly I think it's just Nintendo fans who are salty about these games (big Japanese games like KH,MH etc.) not being on their platform of choice. Because I can't explain the pessimism around these games that clearly have signs of success (a lot of hype etc.).
Trust me, as much as I'd love Kingdom Hearts on Switch, I'm happier than any of you all. Kingdom Hearts is my favorite franchise after Zelda. I've just been so jaded about the whole series leading up to this release because it seemed like it would never come, and the only time I ever heard anyone talk about Kingdom Hearts was to make fun of it, and suddenly Kingdom Hearts 3 is announced after a literal dozen years and maybe it's just the crowds I run in but even the people I used to talk to about Kingdom Hearts back in the day weren't all that psyched for it, so I was pretty jaded and cynical as a coping mechanism. I can't speak for the other naysayers though.