It's more complex than just a base level of whether its a red or blue city. You have underfunded and under supported Police Departments in a lot of these cities, often fighting an up hill battle with the governing bodies of said cities, naturally this leads to a lower quality of prospects because for one no one wants to work a job where their bosses hate them. Not to mention they can't receive the proper training to deal with things whether it be a high intensity situation and how to deescalate, or something as simple as decompressing and working through personal issues after a rough patrol. This leads to the a LEO who shouldn't be in a split second decision situation where someones life is at stake, nor can they effectively know when to pump the brakes and realize that maybe they passed excessive force about a minute ago and you're cruising headfirst into police brutality.
Now onto the constituents of a lot of these cities, a vast majority are low income, and a majority of which happen to be minorities. A lot of these people are coming into a system where the likelihood of them 'getting out' is so damn slim that most will turn to illegal activities once they come of age because working fast food sure as hell doesn't pay the bills. Now because of how our prison and justice system are setup, it's not made for reform, it's made for incarceration and to hobble you for the rest of your life. So a lot of these guys by the age of 20 have most likely been in and out of the system. Either on diversion, straight up juvie, or worst case scenario prison/jail. What options do they have coming out, realistically, aside from crime do they have? Fast food won't hire if you have a felony, construction and factory work? That's not a guarantee and most won't be able to get into it unless they have an inside guy.
While there are community programs that specifically take in ex convicts and people with criminal history that are looking for work and they do an amazing job with helping those people get back on their feet. But to put it simply, there isn't enough of those organizations to really make an impact.
So you have a judicial system whose aim is to arrest as many people as possible to fill out prisons, but not reform any of them. So they more often than not go back to crime. Which leads LE to specifically target those neighborhoods they deem 'High Risk' and the cycle continues. Leading to mistrust and resentment from the populace, as well as the police treating certain groups much more aggressively than others because of the past criminal history of said populace.
Let this cycle continue for 100+ years and you eventually get what we saw in Minneapolis.
There are a bunch of problems that lead to what happened, but two of the largest I'd say is Police funding and training as well as judicial reform. While there's progress being made, no one wants to really have that tough conversation and sit down at the table to hash everything out. How long until the next 'big one'? 1 year?