As a person who grows up in Chinese culture, I think that I can give my opinion for reference.
Unfortunately, I feel it make sense base on my cultural background. I will say this question is about culture shock because major coding community culture comes from western culture.
There are two points which I want to say on this issue, the first thing is about 'Share'. In my personal social experience, we don't encourage share things with stranger especial useful skill (you usually can make money with them). Chinese culture is not an Open culture in some parts.
The second is about business concept and It means that we don't really believe there is a free lunch. Simply saying, you spend your time and knowledge to answer and teach someone who you don't know but you get nothing (reality things or money) back is kind of weird.
Back to the original question, he might just want to ask: why so many people are willing to be volunteers to help others but I think that many people already tell why they do.
I hope that my replication can help you guys to know why this question exist more. Happy Coding:P