Banning of bitcoin by many countries because they want to do full control of currency in circulation so that it could determine economic policy. A simple example is the determination of the interest rates the bank of great impact for the economy.
Most likely that's the main reason why some countries are banning bitcoin because they cannot make income with the transaction as it's not taxable and not transparent enough in their eyes, let's just hope it will not happen as I believe we can get more benefits with using bitcoin that fiat in transaction.
The main reason is the government will not get any revenue from this Bitcoin transaction. And if our govt make this Bitcoin as legal currency then black money transaction will become very easy. So in many countries, this Bitcoin is banned.