system
A chat on subreddit /r/pcmasterrace
human
Most likely because anti-cheat is easier to bypass on Linux.
gpt
Not so much that it's easier to bypass, and more that you'd need to develop the anticheat twice and force Linux users to install either kernel modules or a custom kernel to make modern anticheat work. Because they need to interface with the kernel to do their job.

And of course, they don't seem to work very well anyway as games with a to cheats (sometimes more than one) still get people complaining about cheaters...