The stupid liability laws in most states say that you can not be held liable for not interceding, but, if you do try and help and screw up the rescue, you can be held liable. These clowns took the rule to a whole new level by viewing the victims pleas for help as entertainment, good for laughs.
In China most people won’t help because they would be subject to everything (including arrest and victim’s medical costs). The attitude is that only guilty people will come back and help their victims.
The laws are slowly changing but still not many help and go on their daily business.