Classic textbook example of "bystander effect" in Social Psychology. People stand around and watching these embarassing, humiliating types of events get so shocked, stunned or frozen in fear or terror they either don't think or lack the courage and initiative to help the persons in trouble or they believe someone else in the crowd will step up and solve the problem efficiently. Or that the problem, as it is, will solve itself.
Stanley Millgram's fear and obedience experiments in the early 60's came to a similar, likely more damning set of conclusions that the Stanford Prison experiment did with Dr. Philip Lombardo about a decade later.