I can maybe give you one reason, Police Depts dont care about the concerns of everyday citizens, who they view as little more than traffic revenue.
Complaints to local police depts. no matter how valid or important are often ignored or make a quick trip to the disposal bin. Dirty cops are allowed to keep pulling the same stunts for years at a time. A case in point was a local officer we had in our community. He was widely known to harrass citizens of our town and engage in behavior not becoming a police officer. Including spending an inordinate amount of time with nurses aides at the local retirement home with the key to the medicine cabinet. This was actually reported by numerous people to the local sherriff's office. Their response? No action.
It wasnt until a year later he was caught red handed pilfering drugs out of the towns evidence locker that he was finally fired.
The concerns of ordinary citizens often fall on the deaf ears of arrogant beurocrats who dont care about the people who pay their salaries. It is unfortunate, but it is also the truth.