I understand where you're coming from, but a lot of violence that police encounter is spontaneous and unpredictable.

Say they pull someone over for speeding, but the driver has a warrant for their arrest or something like drugs in their car. The cop begins this encounter expecting to issue a ticket and nothing more, but the driver knows more is riding on the line than that. Violently attacking the cop to increase their chance of getting away might sound like a good option, otherwise they'll spend years in jail for the additional charges they're avoiding.

A lot of this behavior wouldn't exist if our prisons focused on rehabilitation instead of cruel punishment. A simple drug charge can ruin someone's finances and career, which almost everyone agrees is unjust. If they're already facing many years in jail for crimes a cop would arrest them for, what's risking some additional time in jail for a chance to avoid an arrest altogether?

Prison shouldn't be something that people want to avoid at all costs, and the conditions we live in shouldn't push people to commit crime to get by. Currently, our prisons are cruel and our living conditions are terrible, pushing people to steal, sell drugs, and avoid prison at all costs.

Edit: And just to clarify, I'm only highlighting that police encounter violence in situations where people wouldn't expect it. A simple speeding ticket can end with the cop getting stabbed or runned over. Our justice system motivates people to violently avoid arrest, and our living conditions push people to commit crime. So not only do our police need reform, but we need to fix the underlying issues that push people to commit crime and avoid prison to begin with. If that's done, then police encounters that begin non-violently would more frequently end that way too.