Because of the volatility of the price of cryptocurrency right now. It goes up and down way too fast that make a lot of people rich and a lot of others go broke. This fact makes cryptos themselves very questionable about whether they could stay for a long time.
Government of a lot of countries really get afraid of things that are not beneficial and not trustable that could affect their economies.
Because it is a digital currency than the transaction through online, no one can cotrolled it. It can be used for the bad transactions because no one can trace it.