It's more about accessibility. It's not like they make the games anymore and the emulators they have on the Switch are lackluster. You could buy shit on eBay but if it's a super niche game it'd probably cost a lot of money. Money that doesn't go back to Nintendo. It's not like they're going to lose money for someone playing a super rare game on an emulator.

Yeah, N64 speedrunners even went as far as replacing their aging analog sticks with machined steel sticks. Because as the console ages, so do the controllers. And stick drift became a major problem for speed runners who used genuine consoles. There was even a case where an aging controller led to the discovery of a new glitch, when a speedrunner’s NES controller had gotten so old that it allowed him to press button combos that wouldn’t have been possible with a new controller. And that button combo allowed him to perform glitches that would have been otherwise impossible on a console.

The larger issue is accessibility. If speed running requires a genuine console, it severely limits the number of people who can afford to participate. There would be a big financial barrier just to buy the console and game(s), and since no new consoles are being made it will inevitably lead to the death of speedruns as consoles die out and nobody can continue playing.

One of the original goals of emulation was data preservation, since it quickly became evident that game companies wouldn’t bother preserving their own games. And as consoles age, that will only become more and more important. I personally have backups of all of my legitimately purchased Nintendo games. But that’s only because I enjoy data hoarding and have a NAS that can actually store all of it. Not everyone has that luxury, and it means that (again) there will be a big financial barrier to anyone wanting to be able to play the games that they legally purchased and have the right to play.