In my opinion:
1) Anonymity. Actually btc is using by drugs, weapon dealers; terrorists etc.
2) People will invest a lot of money to cryptocurrency, instead their currency. Why you should invest to $, euro or gold, if u can invest money to ethereum or btc and make it x2 or x3 for 1 year. After that economy of country will depend by cryptocurrency, ofc goverment doesn't like it.