because they don't know how to demand taxes from this, and still fear for the economy of the country
They also fear that people would really put all their money to bitcoin not on the bank. As they cannot touch bitcoin they would probably banned this. Since it is a decentralized organization and government can't really touch them all they have to do is banned them. I'm afraid when it comes to our country as well.
In case of paper money there are different types of tax which are implemented on money of the people like withholding tax, sale tax or other taxes but in case of bit coin it was a fear that the people will keep all their money in the shape of bit coin so their banks will stop working.
I have to pay taxes in my country if i want to cash out my bitcoins it is not that bad for me because if you cash out a huge amount it does not seem like anything when you pay the taxes form it and it is not only the taxes.
Because some of them used it in illegal activities and its easy of use for criminal purposes like transaction by bitcoin is highly anonymous so bitcoin can become a tool for crimes like money laundering, drug trafficking, tax evasion, illegal payment and many more.
The common view on bitcoin right now is that it is not as anonymous as many had previously thought. At any rate, bitcoin transactions are readily available to anyone to see and analyze, and there are quite a few tools that have been developed which try to track transactions. There is no doubt that special agencies have designed highly specialized and effective instruments for doing just that.
If you want real anonymity with network payments, you should use coins which don't have public ledger at all, for example, byteball. It allows truly anonymous and private transactions between two parties which don't get written anywhere.