Actually IQ is correlated to problem solving which literally makes you a better everything just not obviously by itself. While this case is an extreme example of scaring off smart people there are lots of less direct ways you can discourage them from joining your ranks. Promoting idiots to positions of power and allowing them to erect dysfunctional systems that people l lower on the totem pole aren’t allowed to change, punishing anyone who snitches on their fellow cops misbehavior, and promoting your idiot cronies are all pretty effect and pervasively practiced.