You may as well ask why they put Viva Pinata on the Nintendo DS in 2008. Or Diddy Kong Racing on the Nintendo DS in 2007. The actual reason, I suppose, is that Rare used to have a handheld division and Microsoft didn't have a handheld console. Microsoft have owned Mojang since 2014, yet you'll find Minecraft on the Nintendo Switch, because it suits them to allow the game on the Nintendo Switch. Sure, they're handing Nintendo a game that will sell Nintendo Switches, but they don't seem to mind. Viva Pinata, as a game, would be well suited to having different versions aimed at different platforms. Think Xbox, PC, phones, and of course Switch.