The reason why other country ban cryptocurrencies because its decentralized and they cant control it if you cant control the currency that coming to your state you cant get regular or cant deduct the correct tax to your people. The other reason is some people are using the advantage to do their illegal work, like selling drugs and smuggled stuff. Another reason is maybe they are creating their own cryptocurrency like another country, and they dont want to use the other cryptocurrency that they dont own.
It is still difficult to overcome. And we need more time to change. The main purpose is to accept it and not be affected by anything.
I think the main reason why other countries ban cryptocurrencies because they have no control with it. It is very difficult to control decentralized currency in which if they want to control it they need to regulate it first by lawful means.