Stuff like East Anti Cheat needs to have support for Linux essentially turned on. Otherwise the game won't run even if WINE/Proton can run the game fine. I think a lot of devs don't bother because they don't know Linux in case OS specific support might be required, and the market was fairly small up until the Steam Deck came out.

For an example. A few weeks after the Steam Deck came out, suddenly Apex Legends and a few other games could be run on Linux without anti-cheat issues. The developers just turned on a switch and made a new build essentially.

For the longest of time is Linux users were mostly just told that people use Linux to cheat in games and that's not really the case.

Overall though there is no real reason why anti-cheat software shouldn't be able to work on Linux.

Multiplayer games often use a third party anti-cheat software. Some of them work on Linux, some of them don't. What the previous commenter was referring to specifically is that some anti-cheat, like easy anti cheat has been updated to work in proton, but it requires that game developer push out an update to enable that functionality. Some do, and some (Bungie) have outright refused to do it, and even threaten bans for players that try to play on Linux.

Some don’t even need to. EasyAntiCheat and BattlEye both have support for Linux and it’s up to the devs to enable support (or upgrade to a version that supports Linux). But in some cases, the companies just refuse to support it (Bungie with Destiny 2 for example)