Because Shenume II was on the original XBox?
Lol wut?
The only.... Only logic I can take from this is that you are saying it can be on the Switch because the original Sega Dreamcast version was then ported to Microsoft Xbox. Whilst that's true, Microsoft (namely Peter Moore) snapped up the publishing and distribution rights for Microsoft to port it over to give the console a big name. Unfortunately it was a waste of time in the end, but it was an exclusive deal between Microsoft and Sega at that time.
The deal with Shenmue HD could be argued to be going to any platform yes, but logic would say that with Shenmue 3 being a PS4 and PC only title, then so too will any HD remakes. You can count MS out because YSNET went to Phil Spencer first with the idea to Kick-start Shenmue 3, and we're basically told where to go, so they are hardly gonna go back on their own decision, and also support HD remakes for a future installment of those remakes coming out on a rival platform.
Nintendo? Never had anything to do with Shenmue. Never shown any interest in Shenmue. Will never be appearing on a Nintendo console. It's not rocket science.