Because they fear if all people people of china starting using bitcoin, in this condition Chinese Renminbi currency popularity will decrease. they want to take control over everything. This is why they already banned whatsapp,facebook, twitter, gmail,youtube, pinterest , pornhub etc.
I agree with you . They ban all media and use We Chat only, which is not good because they are trying to forbid everything outside and put false information about the market to make investors confusion