People sue the city and not the cop because laws protect the cop and prevent them from facing the civil consequences directly.
Yes, the laws protect them from civic consequences but not criminal. If you would prove that the cop murdered someone he would go to jail, not just paid damages. But as I said it super difficult to prove that cop murdered someone because all the cop has to say is that he was afraid for his life and he’s all good. He has the right to shoot the moment he thinks his life is in danger. To convict a cop you have to prove that he wasn’t thinking that. How do you do it? He would have to directly say “BTW I know I’m not in any real danger” as he shoots the victim. There were many many cases where a cop shot someone running away, laying on the ground or even sleeping and was found innocent. All his lawyer has to say is that the cop thought that the victim was reaching for a gun. There was no gun at all? Doesn’t matter, the cop thought that there was one.
And than there’s the expert witness testimony thing where “experts” are paid by police union lawyers to testify, that the cop was actually in danger. Ever heard about the “fact” that a person with a knife is dangerous when he’s closer than 7 meters (21 feet rule)? It was invented by one of those experts. It’s total BS but it helps save cops from jail. They will testify that “yes, the victim was running away and had no gun but according to our studies the cop was justified in thinking, he was in danger”. And that’s it, he’s free to go. Many many cases like that.