ok, maybe one of the biggest wasn't hedged enough. but it is still an important reason imo.
There are many more of course:
- Police can sabotage the re-elections of politicians that oppose them, by doing their job worse and increasing the rate of crime.
- Courts tend to favor the police, inventing such concepts as qualified immunity
- An unfortunately large percent of the country is happy for the police to trample people as long as it's the people they don't like
- And more, which the article gets into some of. I'm not a huge 538 fan but its pretty decent