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.

Steam runtime already gives developers a single target rather than having to support different distros individually.

If Steam Deck, the new Steam Machine etc take a significant part of market share, I think it will be more enticing for game developer to release a native version for Linux. Providing a native version should still be more robust and performant.