That’s largely a corporate decision that is out of the hands of the programmers. Generally speaking, security specialists would agree with you. But running anticheat on the server costs server resources, which means you need more servers to accommodate the same number of players. Running it client-side is a cost cutting measure mandated by the corporate bean counters who did the math and concluded it’d be cheaper for the company to spend the users’ computer resources instead.

While I agree that client-side security isn’t the best solution, it’s certainly better than no solution. It’s the same argument people have against self-driving cars. The self-driving cars don’t need to be perfect; They just need to be better than the average driver. If they can reduce the number and severity of accidents that are currently happening without them, then they should be implemented. Even if the solution isn’t perfect. Because an imperfect solution is better than doing nothing at all.