Some of these happens as a result of fear and Because of ignorance, many governments tend to pass laws without understanding and to prohibit things that they consider to be a threat. And although they can not prohibit a blockage, they have every chance to prevent citizens from accessing this technology which they consider as best in the interest of their citizens.
The main reason can be that still most of the countries afraid to turn bitoin as legal currency, they still consider bitcoin as threat to their country, but i think that it is not so, bitcoin can only improve the economy of a country, because bitcoin is currently providing such opportunities to people which can increase the financial status of such people.