I thought a smart guy (I'm not being sarcastic) like you would know why nobody acted.
Why Do We Help Less When There Is a Crowd? | Psychology Today
On top of that,
if a person, or persons, had intervened and prevented Floyd's death, what do you think would have been the consequences for those interveners? The onus would absolutely be on them to prove that Floyd would have died if they had not acted. Of course, they wouldn't be able to prove what would then be pure conjecture.
While people in the crowd were worried that Floyd might die, nobody
knew with certainty that it would happen. As outlined in the link I provided, people in crowds tend not to act to help people in distress. Asking them to help someone in distress at the hands of police is on an entirely different level.
I'm not at all surprised that nobody intervened. I don't blame them and neither should you.