1) Too many people in too small a space, with historically fierce competition for resources to survive. China is simply way overpopulated and everyone is in the mindset of scrambling, even in urban locations and situations where a wealthier population or guaranteed resource (i.e. assigned airplane seat) no longer requires the scramble.

2) Somebody above already talked about this: Fear of each individual that s/he might miss out on what somebody else is getting. Zero-sum game mentality--if you don't get something, you are a comparative loser. Chinese are not graceful losers.

3) An entire culture that is basically selfish and ultimately has little allegiance to any group beyond the family. This is not a modern (i.e. Communist) invention but goes way back in history. Community Responsibility for the benefit of strangers and wider society is an idea that is in its infancy in China...it's starting to take root but will be a long time developing.

Some people would also posit that lack of any religious tradition in the general population has led to an amorality of behavior over the centuries.

I find that Chinese mainlander behavior today is definitely different from that in other developing, non-Han Asian countries. But I don't think it's inherently an ethnic thing per se. When looking at ethnic Chinese only, you can see the difference between the mainland vs Hong Kong and Singapore, which of course have different histories and where British influence set the tone for many decades, even before Singapore existed and even when HK was relatively poor.

I will say that as far as Beijing goes, queue behavior in public places is generally better than it was several years ago, and I think some of the behavior-modification effort put in before the Beijing Olympics stuck. Not perfectly, not completely, but there is now a significant segment of the Beijing population that is capable of more "civilized" behavior...if they feel like it.