China has a lot of miners that helps to maintain the network of bitcoin. And this is why many aren't liking it if the gov't of China will disable their people to mine bitcoin. You can shift to other countries like other miners did but there's sort of difference why it is a good place to mine in China. There are factories alike if you will look outside the warehouse but inside of it is a mining farm facility. If ever the difficulty drops, it will increase suddenly which will be taken by other miners.