"The purpose of a system is what it does." The purpose of police is to maintain current structures of inequality, and to divert, undermine, and oppose mass movements that could lead to a radical upheaval of those structures.
It is effective at that! Its incentives are already aligned with the forces that have the most influence and mutual benefit with them. It is working as intended.
This is one of my favorite modern conspiracy theories. Shea and Wilson did it better back in '75 if you ask me.