A second-hand Windows 10 Pro license costs like $25 (and used to be $5). That's a pretty small price for a substantially better experience.
Like, if you want to pirate software, go pirate software. If you're going to pay someone on a per-install basis for pirated keys, I'm gonna laugh at how easily you're being taken advantage of.
But depending on your jurisdiction, the $5 enterprise keys can also be entirely fine. Sure, in a way that's outsourcing piracy. But the law doesn't have to see it that way. There's nothing illegal about buying enterprise keys, and if they are overprovisioning keys that's between them and MS, I can't even know if that's the case.
That being said it is difficult to shed a tear for Microsoft of all companies over this practice.