You'd be talking about suddenly adding support for every game they've ever made running on a million unique hardware configurations. There is literally only downside for Nintendo's brand in doing such a thing.
"I want 120 FPS. Or it's suboptimal!"
"I want an AMOLED, not just OLED. Or it's suboptimal!"
"I want keyboard input. Or it's suboptimal!"
And on and on.
A console generation is 8 years, on average. Nintendo's approaching the end. If we're making fun of Nintendo because a smartphone is more powerful, that's a testament to how fast phones have become, not a testament to Nintendo's sluggishness (as the Tegra X1, at the time, was the fastest mobile graphics chip available. What are they going to do? Call the generation after four years?)
Emulators are the antithesis of performance consistency. I love them, but there's zero way Nintendo (in its current form) ever officially supports an emulator you run on a typical PC.
Yuzu also has things that just don't work well for most players. Super Mario Odyssey depends quite a bit on HD Rumble; which a Yuzu player almost certainly won't get unless they use a Switch controller. But why would an emulator user buy one and not use the Xbox controller they have lying around?
Yuzu also tends to fuzz the timing for complicated games in weird ways. I saw an emulated copy of Super Mario Bros Wonder someone was playing, and I tried a very hard level (5-out-of-5 difficulty) called Fluff-Puff Peaks Special Climb to the Beat. Super tricky (https://youtu.be/4PcBDeCKa0Q).
On my Switch, I could beat it on a few tries, consistently. On his emulated version though... I could not beat it. I tried over and over - with a Pro Controller - and could not beat it for over an hour. I pulled out my Switch version, again, a few tries, beat it. I swear Yuzu was subtly, imperceptibly screwing up the timing and physics. It wasn't a slow computer either - 13th Gen i5, RTX 3050. Not the latest thing around, but should be fine for Yuzu.
I haven't used Nintendo Switch's Online emulation service, but my understanding was that the N64 emulator for it was initially very bad (though I've heard they fixed it?). On emulators for Windows, playing the same game, they would boost the resolution to 1080p [1] and bump the frame rate up to 60fps for a lot of games, while not giving any real negatives. For example, I think Conker's Bad Fur Day plays much better on Project64 than the original cartridge, so I'd define that as "optimal", and probably better than it would be if it were on the Nintendo Switch service.
EDIT:
[1] Actually I could be off on that number. I thought it was 1080p, but I think that doesn't jive with aspect ratios. Still, it's a higher resolution than what the original hardware gave us.