Games very much are using server-side statistics analysis for cheat detection. Valve made a presentation about it and Epic has an API for feeding game state data to ML anticheat for aimbot detection (game-specific and in addition to their existing anticheat measures)
Either everyone on Earth who’s working on this has a skill issue (which is probably hubris?) or there’s not enough differing humanized enough aimbot from human aim (note: Valve manages to screw up even here, with cheaters in Premier basically rage aimbotting these days IIRC)
In addition, there’s not much these things can do against subtler stuff like ESP.
It’s just that it doesn’t work.