Because this system isn't region locked Nintendo and Capcom could just save some serious cash as well by only releasing it in Japan and we could just port or download the game. It's a fighting game so the language barrier isn't a major hurdle by any means. Just like playing a port of Street Fighter. You know, this is an option if they wanted to go the thrifty route. But if Nintendo was able to get the rights for Capcom once they can do it again for an international release.
Another question is if this became a Switch exclusive and we could pick one guest Nintendo character added to the roster who would be the best fit with the Tatsunoko esthetic? Off the top of my head I'd go with Samus or perhaps even more suited would be an F-Zero character.