China has a lot to lose if they would allow even a smidgen of freedom for their people. Once the Chinese people get a taste of freedom, especially financial freedom through cryptocurrencies, they will definitely want more. And this is completely contrary to the ruling party strategy of controlling their people down to the tiniest detail. So obviously they will do everything in their power to prevent this. Not that they can, fully, with crypto. At some point the "ban" on cryptocurrencies will show cracks and more and more information will leak out about the world adopting cryptocurrencies. They cannot stop it.

All they are doing is prolonging the inevitable and losing out on profits from taxes.