Why is Chinas stance on bitcoin and other cryptocurrencies watched so closely?
Because they are the country who cares about the future and thus are trying to control the situation because it is better that way than for it to get out of control and then they will hit big wall. If you look for instance US is also closely watching what's happening and EU. China is aware that this whole thing can disrupt the money system that was built before and questions such as how you tax it, who to trust etc. should be asked. To my understanding China is mostly negative towards ICOs because of the way they are funded and because there are scams related to it.
China has never stepped behind when the matter is about technology and development and has been major market for most of the technological inventions. China has major investors and people that dont want something revolutionary thing such as crypto currencies go to vane. So china is regulation crypto currencies and protecting its investors from scams and ponzi schemes.
Recently china also created a fire wall and blocked people access to outside crypto exchanges to ensure that the money stays within china and is not flooded out. And not only china, almost every country is getting against ICOs now as most of them are scams and they are not being registered under government to help protect people from losing their investments.