Perhaps, the main reason why some countries are looking to ban bitcoin is because of their current economic system. Bitcoin is decentralized, government can not put a total control on their economy if they are using transactions coming from sources that are beyond the control of the state.

Bitcoin main purpose is to allow people escape the central banks money manipulation happening globally since centuries. Some countries haven’t still legalized bitcoin, because it is  allowing more freedom to people, and people are actually using that freedom of course. They are using Bitcoin for its purpose: to save their wealth from external manipulation.

Thats one of the top reason why government not legalized bitcoin yet.
The other reason is because government think bitcoin is too risk  investment.

Some countries still have not legalized bitcoins because it is direct money for the people from the companies and there is no interaction between government or any legal body of the country. So ultimately the govt wants to have some part of the money as tax and there is no tax policy against the bitcoins. So its an opportunity for all of us to invest in bitcoins in which there is no role of government.

Well, Bitcoin have a lots of persecutions because of its use. Bitcoin is now used in illegal transactions, the thing that we did not expect. In some news about cryptocurrency, Many porn sites are now accepting bitcoin as mode of payment if they wanted to take a girl. As we can see, Bitcoin is just a digital currency but many people are crazy on it. They use it in pushing and selling/buying illegal drugs and scamming. And this is still continues so that many countries banned Bitcoin.