It's a bit of a grey area, and it's not true that Nvidia needs to have a licensing deal. It's definitely against the license terms you get when you purchase a game through steam to run it on arbitrary hardware, but most (at least EU) courts would probably hold that if you own a game, you can run it on any hardware you have access to.
What happened was that when Nvidia just got started, they had an opt-out framework (for developers) instead of opt-in. At the time, some game developers felt like Nvidia was profiting off of their work unfairly, and posted publicly about it, and there was a decent-sized backlash.
However, in the meantime, other competing streaming platforms have gone with opt-out and there hasn't been much of an issue around it. I think most developers have come around to the idea that it increases game sales.