I think the main reason is disadvantages of cryptocurrency
. You should know that cryptocurrency is being used so much in dark market and by crimes. Beside there are a lot of people wanna take advantage of cryptocurrency to commit guilty like money laundering, tax evade, selling drug,....I think these countries wanna prevent this problem so they banned cryptocurrency
If they want to prevent drug selling and tax evade they should activate structures that fight against drugs spreading and different tax services that should control all such money movement. Cryptocurrency is not the magic tablet and with lack of crypto there will not be lack of criminal.
Criminal uses dollar to money laundering, lets ban dollar, ok?
Terrorist uses toilets, lets ban them, ok?
There are other reasons for governments to ban crypto. And the main is possibility of crypto to equalize the difference between rich and poor people. They afraid of it. People become smart(imo), and this is a problem for them. So they "ban" the community this way. But what they are expecting from this action, or they would like to ban the whole internet lol