Why is it not more common to implement anti-cheat on the server instead of the client? Is that not more secure? Couldn’t the server just check what vision a player should have and not provide any other information to prevent wallhacks or maphacks? Or check how fast it is possible to move to prevent speedhacks? Aimbot is a bit harder to detect I guess but what about the other ones?
They usually use both. Client side and server side detection together.
The problem isn’t the check itself usually, but rather latency. If you shoot a player on your screen you want immediate feedback (client side), instead of waiting for a roundtrip to the server until the blood spatters.
There have been shooters where the server decides if a bullet lands. So on your screen you hit the player and then they suddenly survived. So most shooters switched to: If the client thinks it hit, it hit. Which does lead on the receiving end to running behind a wall and still dying. Overall it feels better than the alternative though.
The whole topic is pretty much game networking, it’s a balance between doing it correctly (server side, slow) and faking to get it close enough (client side, immediate, easier to cheat, unfair if the player is laggy).
Of course there are some server checks that are always easy: For example if a player teleports or moves around the map faster than possible? You can flag them for review or if it happens too often kick/ban them. As long as you’re super careful about automatic bans (bugs exist).