The police-citizen interaction is the only one where no one dares intervene.
George Floyd died in public. There were citizens watching as well as other police watching.
If one citizen was trying to kill another in a public place, I'd call the police. I'd get involved physically if someone's life was at risk, and I thought I could help without endangering my own life. There are lots and lots of people who would intervene to try to save someone's life, by themselves or as a group.
But when the police do something wrong, what are you going to do? Call the police? Try to stop an officer from killing someone, knowing that you could be in the same position yourself if you try? There is no other comparable situation.
So people stand there, pulling out their cell phones to make a record of what is happening. I can't imagine watching a murder go on right in front of me and knowing there was absolutely nothing I could do to help that person. And I especially can't imagine it at age 17, which was the age of the girl who made the video.