I’m going to do a hard disagree here - they don’t have to support Linux, just add compatibility in terms of anti-cheat for Linux. Proton is likely good enough to run the game itself but the anti-cheat sees Linux and just craps itself.
They don’t even have to provide support - League of Legends runs on Linux if you install the game using community scripts and custom proton, and while the client runs poorly nobody spams the Riot Games support about how the “Linux version” client doesn’t work the well because people understand that it’s a community effort. Riot themselves have only made a statement saying how they’ll try not to break the game for Linux users, and that’s pretty much it.
League of Legends is a massively popular game as well, yet Riot barely has to do anything to maintain it on Linux, let community fix issues that come up, let community provide support as it’s their tools.
And while I do understand that porting an anti-cheat to be more friendly to another operating system isn’t an easy task (such as for Rust, where they tried to make the anti-cheat compatible with Linux but it introduced other issues so it got shelved), I think you’re vastly overstating the amount of areas a company has to cover for a game to be playable on Linux.