It helps fight their inflation (surplus CNY) problem.
It gives their citizens something of value to invest in.
China produces all the Mining gear
Chinese government is probably doing all the mining, after-all, only large scale operations are now capable of serious Bitcoin mining.
All China's top companies were getting on board.

One month later, we have a perceived Chinese Bitcoin ban 3 weeks around the corner cos:

Bitcoin facilitates capital flight from CNY into global currencies (with hindsight, were The Peoples Republic of 'pegged to the Dollar' ever going to allow this shit to spread unabated?)
It allows China's citizens to operate off the financial radar
All China's top companies are dropping it like a shit covered brick
Government is telling top retail websites to stop selling Mining Equipment