Google suggests that there are some 1 million law enforcement personnel in the US, so even if only 10% were total assholes that’s still 100,000 assholes that you might never meet, depending on where you live and how they are distributed.
In practice the assholish behaviour is more likely to be structural than personal, making the distribution even less balanced; so you would expect that some people will meet only asshole cops and others would meet hardly any.
Quality and aggressiveness of law enforcement varies significantly within the United States, and I don’t just mean state-by-state, I mean town-by-town.
I lived in a professional suburb growing up, the kind of place professionals move to when they want to raise children. We didn’t have the shootings, framings, etc. We also didn’t have much in the way of crime, and town revenues were not a problem.
But then you have other places where the town is running out of money as density collapses and decides to loot the population to stay afloat. Or places in the inner cities where structural problems lead to severe cyclical poverty and no one with power cares about the police not being terrible.