Some of the countries or their governments are very conservative and they reject all attempts to break or bypass their conventional economic system. And they simply ban bitcoin or all other digital assets.
Despite the advancement of technology these days, there are still some countries who still do not accept this kind of change. Some are afraid of the harm it may cause to the citizens and the country itself. They might see it as a threat to their economy. Some countries may seek new ways to cope up with the growing technology but there are still who do not want to take risk and better remain with their traditional currency.