1. I think China want to temporarily crash the market so they can collect more BTC (and other coins dirt cheap) before announcing that they are officially adopting. At that point BTC (and other crypto) will sky rocket.
2. They don't want their citizens to trade cryptocurrency and earn (relatively easily) in fear of losing their cheap labor force. They will then try to make it as difficult as possible for it to flourish in their country.
Which is it???
could be, because China is very insistent in terms of economic development of their country and their main enemy is the United States