It's not that, it's that the experience wouldn't be the same or of the same quality so it would hurt Nintendo's image.

You can run a Wii game on not a Wii. But if you're not standing in your living room with a Wii remote, then you're not playing the game as it was intended. You might have a shitty experience and that reflects badly on Nintendo.

Same for something like a DS. Yes, you can emulate a DS on something that is not "dual screen". But the form factor, dual screen, and stylus is integral to the game's experience.

Nintendo isn't like Microsoft or Sony. Thier games really lean into the hardware and rely on it, and it does genuinely allow for a unique experience.