I'm also super happy that devs are embracing Linux — Proton and native — thanks to wanting to make sure their games work on a Steam Deck *somehow*.
Linux definitely isn't a lot of the market share on Steam, but it's still the second largest, under Windows and above macOS.
Also: Some games run so well in Proton compared to natively on Windows, that Windows folks are pulling pieces (like DXVK) over to Windows to get the games to run better (or at all).