why is the forum in china don't to create revenue for users?

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it's the wave in relationship and communities ,we know it has the creativity and culture.but there are many contributions to the value of the users ,like bbs or forums or web2.0 wedsite.if they succeed,the users don't get any benefit!so why?this is the result of different environments. however,in such site abroad ,like forums or web2.0 website ,it will enable us to make extra money,like mylot,but in china is no,who can tell me why? if you have good ideas ,give reply that let's me konw.ths! good luck!!!