I'm American, and lived in China for two years. It's common to see things on the street that you don't understand, even for natives, and it's not prudent to take what you're seeing at face value. There are lots of scams, so one's first instinct is to hang back and protect oneself. Those times when I did get involved to ask if people needed help, it was always somewhat coldly and hurriedly refused, probably because the people I was offering to help feared that I was up to something. At the risk of making a racial/cultural generalization, Chinese people do not trust each other as much as Westerners do. I wish I understood this phenomenon better.

And, at least in big cities, there is so much going on, and so many people. Surely this makes bystander effect much worse. I like to help, but when problems happened, it was almost always the smart thing to do to just get out of the way.