Well I assume there are ways to prevent that (or make it extremely difficult at least)? E.g. look at denuvo, nobody has been able to "open a hex editor" and disable denuvo.
In fact, three people have been able to do so, that's why denuvo games do get cracked.
That's not even the point though, I am not saying it is literally impossible to circumvent this, but as long as it is hard enough that it is not financially reasonable for the cheat makers, that's good enough.
Anti-cheat systems, on the other hand, are entirely different. If you only need to modify one variable in the game, it's much easier because, in most cases, that variable is frequently used. This means you can't add too much overhead to its use, and after all, it's just one variable.
>Denuvo isn't just a flag on a process
Nor would be PC's solution. That's why they added it, making it relevant.