Rocketman:
It's a combination of fear, and the "don't get involved" culture that we live in. It is easy to say what you will do in a given situation, and quite another to react to same. I'm quite sure that those students were gripped with fear. Look at the one's who did react. One was a holocaust survivor who lived through unspeakable horrors, plus life behind the iron curtain. He gave his life because he had the courage to try to help others.
Young people today are taught to "work it out and or talk to each other". They are not trained in defending themselves against nut cases who are not interested in "working it out". Additionally, they do not want to get involved in other issues due to the law suit crazy society that we live in. Sad, but true.