Nvidia are making money by selling you access to a publishers games.
Nvidia is selling access to a virtual machine that is capable of playing video games. They are not selling access to the games because you already own the access to the games.
Lets say Nvidia is a car manufacturer and that video games are a "car amusement park."
Nvidia sells a lot of parts that people can put into their own cars. Those people's cars can go to the car amusement park as long as they own a pass for the park. And plenty of people already have cars that go into the park.
But then Nvidia decides one day to not only sell parts, but to rent out super cars to people who want a better experience at the car amusement park.
Now, when people bought the Car Amusement Park Pass, they knew that there would be some rides that their car couldn't handle unless they had a super car. And they can use the Car Amusement Park Pass if they bought a super car outright.
So if Nvidia is selling you a super car that you can use at the Car Amusement Park, the very Park that you already own a Pass to, are they selling access to the park, or are they selling a better experience that Car Amusement Park Pass owners already paid for, but couldn't previously access because the car they own outright isn't as powerful?