Proton does such a good job that it is difficult to justify the cost of porting games when they already run on Linux in Proton. That said, Feral Interactive is still porting games to Linux and they have not gone bankrupt:
https://www.feralinteractive.com/en/news/?platform=linux
Proton often runs games better than the native ports, so there is not much of a loss if there are fewer native ports. Furthermore, in a number of cases, Windows games actually run better on Linux in Proton than on Windows.
Elden Ring is a fantastic example, as on day 1, it performed about 15% better on Linux in average FPS, and had substantially less stutter if I recall correctly.
World of Warcraft is another great example. It is well known to get about 20% better performance on Linux than on Windows:
https://www.youtube.com/watch?v=V2_LlSaYNUo
Minecraft is another such game:
https://www.youtube.com/watch?v=ytgDMgYL0eo
If you use AMD GPUs, it is more often the case that Linux will outperform Windows in games, since Valve wrote the shader compiler used for them on Linux and it is fairly amazing:
https://steamcommunity.com/games/221410/announcements/detail...
Nvidia is working on improvements for the performance of Windows games running on Linux too. A recent driver release mentions a few such improvements:
https://www.nvidia.com/en-us/drivers/details/237587/
Not all games perform better on Linux than on Windows, although Valve has people actively working on changing this:
https://github.com/ValveSoftware/Proton/wiki/Changelog