There’s just no way to stop cheating client side despite what devs love to think. But server side anti cheat is much harder and requires more work; it’s much simpler to just install spyware / rootkits on the client and call it a day.
As mentioned in another comment, you can’t do this on the server without expensive checks for every single player that is always checking line of sight, because it’s not just your session running on a single server but multiple sessions.
And let’s say you did this, now you have a latency problem because most modern games to make them feel fluid has client side prediction with server reconciliation. This is what makes your modern games feel more responsive, if you put a constant server check there you have lost this.
No matter what people say online, it isn’t just move all of it to the server, there is data the client needs to know and can’t be spoonfed by the server.
Why would a company pay for anti cheat infrastructure when they can outsource it to some company and blame them if there are cheaters or upset users? Windows is the status quo too, so it’s very easy to point to everyone else when justifying your choice to the execs.
It would be great if steam deck+box start costing studios quantifiable amounts of money that can be used to justify fixing this instead of outsourcing and hand waving.