That book was so far ahead of its time, even compared to modern popular understandings of history. You’ll see plenty of people today criticize the hypocrisy of the founding fathers, but Zinn went deeper than that. His analysis of the actual interests they were fighting for, and how this didn’t include most Americans is profound. I love how he highlights the conflicting interests throughout American history that are usually downplayed in popular thought.
I mean, police funding is done on a local level. If you’re asking why most cities have continued to fund their police departments despite rampant corruption and abuse of power, that’s a pretty complex issue. You’ll probably want to start by looking into the power police unions have, that’s a major issue for anyone trying to get police reform and accountability.