I work in games (formerly AAA).
Chicken and egg problem.
Valve is making enough headway that game makers take Linux seriously. We’ll likely see a lot more native releases over time. (once the worry about anticheat subsides).
And still why should normal people go to Linux over Windows? Linux support is still not that great from OEMs and for the unwashed masses your local Best Buy or Apple Store.
Why bother making native releases when Valve/Proton will take care of it? Who wants the headache of supporting another build and directly supporting N flavors of Linux distributions?
When it comes to games, Linux has an OS/2 problem.