Because he doesn't like sales? Why would you intentionally limit the reach of your game? Unless it's going to rely on motion controls, which means it'll suck anyway.
He's never cared about sales. He just chooses a system that he wants to release a game on. No more heroes was on Wii originally and it sold ok even though it had a crazy install base. Just because it could be on ps4 doesn't mean it'd sell well. Sure it has the potential to sell more.
Basically it's because of the Switches hybrid console handheld capabilities and motion controls.
Because he doesn't like sales? Why would you intentionally limit the reach of your game? Unless it's going to rely on motion controls, which means it'll suck anyway.
If the rumour is true then I'm glad he is not deciding to make a game in the style of NMH 1 and 2 because those games have aged very poorly.