Most of the time, you'll hear government officials stating that cryptocurrency is a "high risk asset without any guaranteed returns" and is "prone to be used in illicit activities" while on the contrary, fiat also exhibits the latter largely. I don't buy the government's reason as to why they are trying to ban cryptos or to get their citizens' hands away from it. It's true that it's easy to launder money using cryptos but don't they know that fiat is easier? The difference between the two is that bitcoin's faults are publicized while fiat's aren't.
Or governments do it to protect their own citizens against these "bubbles", which one could argue is a lot of bullcrap.
Bubbles also occur within registered stock exchanges so I don't see why anyone would buy that reason honestly.