[Risord]

Because knowing which data is hidden by UI from server is hard problem.

To achieve real-time feeling game apply (most) your inputs immediately without having to wait relatively long time confirmation from server. So if you decide to push button and peek around corner you expect to see enemy immediately but server will know about your peek "much" later.

You can for sure limit some information by locations but you always must leak more than it's actually seen by client. Also it isn't easy to solve: can any part of volume be seen from another volume inside arbitrary 3D environment. Enemy size and movement through network frame => players all possible eye positions.

I think current best solutions rely on very rough (manual?) map piecing. So is it worth to invest for such thing that makes some cheats bit less powerful but cannot really prevent them.

[mrguyorama]

Keep in mind that CS:GO is ALREADY built on very very old BSP maps, so knowing that some players aren't visible to others is super trivial, if not 100% accurate (ie it's a little conservative)