It is bystander effect. I have been victim of it also. When I got in to a fight after school and they banged my head really hard against the wall, I started bleed and passed out from the hit. It took few minutes for other students to realize that I wasn't moving before they bothered to do something.
There was just the same kind of enrage on the local shit papers (local- and tabloid papers) and student blogs.
But yeah, human psychology is complicated and dark thing. They can watch their friends and loved ones die front of them and stand there without shedding a tear... and we can predict when that shock will hit the person quite well.
I am not going to take a enrage because it was a toddler who got hit* (* I don't see age to be a factor when it comes to estimating the value of humans' life). I am going to take a hate a rage because of the predictable human mind is in it full glory again.
Life is what it is... But still where was her parents? the fact that bystanders did nothing is bad, agreed. But the fact where was her parents - they should be looking a toddler constantly.
Beside, the attitudes and behavior Chinese people have due to their culture, country and politics are what they are and forge people who have different sets of behavior patterns and triggers. Welcome to world of cultural relativism, a world that is grim and dark and in which we must let horrible things bass by because... we must. It is easy for others to take a rage and specially Internet bloggers to write things about the event. But let me ask you, how many of you would been there ready, willing and able to help her? And don't lie just to keep your self-image up. If I'd been there I would most likely gone to shock and had to take time before I could have helped her. It is easy to afterwards "Well this is what I would have done". I been trained and educated to help victims of different accidents, but I know, that I wouldn't be able to act instantly, I would need time to start doing something.
I don't know what they teach in Chinese schools about how you should act in case something like this would happen, but I am sure that they do not teach the same attitudes and methods as they do in west.
So please people don't act all high and mighty, and think "this is what I would have done" when I, you and everyone else knows that you are not most likely going to have the "spirit" to act instantly. (Note: I do not assume that you would just walk past ignoring her either), but if you do, !GZ! you have a good human "spirit" and have most likely seen something like that happen earlier in your life and were unable to help.