Because bitcoin threatens the status of paper money in my country.Bitcoin is not controlled by any person or any government,also bitcoin is always used for illegal activities,so the government banned it.
It not actually threatens the paper money .The government will wont allow this to happen to replace the paper money.
Bitcoins will remains as other form of payment online ,a digital currency and with that advantage the disadvantage on paper money is having tax unlike bitcoins with no tax so the government have no control over bitcoins. Illegal activities or transactions is not a big deal for them to banned it .The only main reason is the control of currency by which government use to earn from our taxes.