The main reasons why some countries doesn't want to legalize bitcoin is because of it's volatile price in the market.
And it's anonymous feature that you cant track where the payments came from or a person's source of income.
Yes, many are afraid that in a few years he may disappear and do not want to bother. And they want to keep track of all operations.
The reason the government does not legalize bitcoin is not due to fluctuations of bitcoin But decentralization. It makes the government can not control bitcoin. That's the main reason dude