In my opinion, as the bitcoin is a decentralized currency, and control of the state in fact can not. And China is a rigid centralized state. I think that's the reason for this
The introduction of new digital currencies , has rocked the social and economic order, creating hidden financial risks and, in some cases, fraud. This has warned the Chinese National Internet Financial Association.Chinese regulators are preparing new ICO rules and may ban them entirely until the law enters into force.