Another reason is that they think that bitcoin or crypto is disruptive in its only little way. But I speculate that they are just throwing out reasons, but behind they are afraid for something that they can't really get a hold off, specially crypto has started to boom last year. Millions of cash flowing and they can't even control it.
I say Bitcoin and crypto currencies are well disguised HYIPs (High yield investment programs, 10% after 10 days etc..)
GTFO. Shoo!!!!
With so many people investing in Bitcoins in which the government cannot take income tax and transactions are anonymous, the government is simply allergic to such decentralized monetary system.
If the concern is tax, then China could simply put tighter regulations around it. Bitcoin is not anonymous per se, heck, they can even track Chinese whales if they wanted to. They are afraid that it might take over their economy and disrupt it, but for me the only reason is that crypto cannot be controlled. Simple as that.