In an ideal world everything would work out, but for some business it is a pretty huge commitment for what was less than 2% of the market just a few months ago. We certainly lost money porting our game in Linux at that last place I worked. It was before Proton though. Obviously each case is different, and some games work on Linux out-the-box due to Photon so this become a non-issue.
Not sure I want to name the game because this would make me very easy to identify from my post history. It’s a game on Steam that sold over 250k copies. My boss promised a Linux version very early on because they thought it would be easy, but we ended up being stuck with that promise.