Harry was billed in early books as this "Anti-Voldemort", who'd lead Wizardy to a gilded age and do great things... But JK Is a Status Quo loving Neo Liberal and can't imagine a better world. In all of her works the system is corrupt, but it's fine because the only thing that would make it go wrong is one bad faith actor (In this case Voldemort), who will stumble upon some obscure rule that undoes him. (In this case, killing Harry who was at that time the last horcrux)
Harry becomes a cop and doesn't change the status quo because the world as it is is the best JK can imagine it.
It's kind of like how no one did anything about Trump, they kept waiting for him to trip over some rule that sends the system crashing down on him, but it never happened.
It never happened because the system is powerless to punish anyone, because the system is just an idea, it is immaterial.
The Electoral College isn't going to magically vote for Hillary because it recognizes Trump's evil. People have to recognize his corruption and change the system to combat it...
The Democrats never learned they couldn't just wait for the System to punish the Republicans after they accumulated enough good/bad boy points