One perhaps slightly sensational idea might be that the Chinese government are themselves investing in bitcoin and levering their position to manipulate the value for gains. If you were an entity with the ability to knock 50% off the value of a commodity, then on a whim double the value back up again (ie, you're the Chinese government with the world watching you to decide on speculations), this is what you'd do.

This is why when some above have said "the government aren't that stupid, these remaining exchanges have their days numbered", maybe they have allowed them to continue trading because they don't want to destroy bitcoin, rather play with its price for gains/further understanding of the market and the demographics of its users.