China believes that if you invest in counterfeit currency, if you are scammed, no one can help you get it back. If you invest in fiat currency, the government can help you get it back. It may also be that the Chinese government feels that it cannot control cryptocurrency and has implemented a policy of prohibiting mining, but the country is generally for the benefit of the people. It cannot be said that China's approach is completely wrong, but it is obviously not very smart.