I attribute this to living under an authoritarian government that supposedly takes care of dangers to society. We're just bystanders and taught not to meddle because the police will take care of it.

I've lived in different countries and have seen different reactions where people are used to feeling responsible for their peers because they know the government doesn't care, is not efficient, or otherwise limited.

Of course, some people will also be reluctant to get stabbed for a complete stranger.