The main reason is the fear of these countries about the volatility and uncertainty of the digital currency. In addition, as quoted from bitcoinbans.com, another reason is the fear that digital currencies will be used as financing for terrorism.
They didn't even start making these advances at regulating bitcoin just yesterday but its been there since Adam but they haven't suceeded and i don't think they will because terrorism has been in existence for a long time and there was no bitcoin so it means fiat currencies can the same way be used to sponsor such terrible acts so we shouldn't single out bitcoin alone.