You can still detect that stuff on the server. It's all about will and competence. The real reason is anticheat allows easy surveillance. The Ven diagram of people with Tencent anticheat and essential IT personnel overlaps a lot. This is a big problem talked about but not solved in sec ops.

Detecting the angle, acceleration and speed at multiple points of a shot in an fps is trivial, and developing a check to see if it's human movement or computer movement is easy after that.

Aimbots are easy too. Is the camera following someone without having vision? Oh no aimbot. A bit more complex than that... But not by much.

It's easy enough to do it right, but then you don't get that sweet sweet surveillance