Nintendo is in an interesting position whereby they are actually selling emulators as a product to this day. Which gives them more of a leg to stand on in these sorts of efforts, regardless of whether or not I personally agree.
Can’t distribute games or other copyrighted software with them, though. Of course that’s still highly likely to get you in trouble. And with the same caveat as anything legal in the US: it’s as legal as your ability to weather a series of failing lawsuits against you.
Seems like emulation is only fine if they make money out of it.
And then emulation isn't stealing anyways.
Or it’s just different corporate policies at different times being applied inconsistently.