While previously you've been able to play League of Legends on Linux, and there's some pretty die-hard fans using Wine to play it, that's set to end soon with Vanguard being introduced.
This also applies to Valorant. I know a lot of people look down on both games, but it's still unfortunate for Linux to lose access to such a popular game.
I thought this part was particularly interesting:
Half of anti-cheat is making sure the environment hasn't been tampered with, and this is extremely hard on Linux by design. Any backdoors we leave open for it are ones [cheat] developers will immediately leverage for cheats
That's pretty much the only reasonable explanation at this point. If they were afraid of people finding errors it would be beneficial to allow more players to see what's the program doing. Riot basically confirming they just want to run spyware on SpywareOS.