I think it has to do with the type of government that they have. Their government system wants control over the people and with bitcoin decentralized and anonymity design they will lose the control of their population. Also it might be just a marketing strategy of chinese to make the cryptocurrency drop its value more and when it is very down they will buy almost all available share of bitcoin investment. So if this speculation is true the drop is just for a time and the market value for bitcoin will grow exponentially soon!