police pensions
While qualified immunity and policing culture are significant reasons for the continued violence at the hands of police, another factor is the money.
Police get generous overtime pay, so booking an arrest near the end of a shift means they bank time and a half for doing overtime to do paperwork, talk to the DA, etc. This is time consuming but easy work, so they are effectively rewarded for pulling in an arrest near the end of a shift. This is also one of the reasons why police budgets continue to expand even if crime is not getting worse.