Linux is becoming more and more popular on the desktop because it is now well suited for gaming. In addition to Proton, you also have to consider all the handhelds like SteamDeck. Valve certainly doesn't want an Nvidia product with crumbling proprietary drivers. With AMD, Nvidia could see that there is a market for it and has now established itself. It was only logical that Nvidia would not stand still. They will do everything to dominate the market as well.