You tell the server you're on the other side of the map and it just trusts you. Teleport hack. The other guy is on the other side of the map and behind a wall but the server is still sending you his position. Why send the client information it shouldn't have?
They want to pwn your computer so that you can't tamper with the game. They should fix the game so that tampering with it doesn't matter.
But there are some cases where you just have to rely on client side. Like when other player position is partially obscured, server have to send it's position but it might be almost not visible by naked eye.
Teleport hacks are unfortunately also not that simple, I think most of games do not trust client input but give some wiggle room for network latency, that can be exploited (it should be limitted to reasonable amounts to allow max like 200ms or so of latency)
Most "pro" cheaters (there is market for this stuff) use protocol level tools that are invisible to anti cheat software as those work as proxy on physically separate computer.
Wouldn’t be a great experience though. Especially not for a competitive game.
> They should fix the game so that tampering with it doesn't matter.
By making it effectively unplayable?