I could see it happening because governments think/ fear it will only be used to either launder money, or in illegal activities. Also, there's huge amounts of FUD's and speculation, i have yet to see any democratic country issue a full ban on crypto.
Or governments do it to protect their own citizens against these "bubbles", which one could argue is a lot of bullcrap.
Quote
The Central Bank of Indonesia warned its citizens in a press release over the weekend which led to the voluntary closure of two cryptocurrency exchanges.
The statement read: Virtual currencies are vulnerable to bubble risks and susceptible to be used for money laundering and terrorism financing, therefore can potentially impact financial system stability and cause financial harm to society.