Their countries , their laws. It really depends on your definition for not supported too . If we speak about banning then as far as I know I don't think there is a country that actually banned bitcoin , at least nothing official and If there is then Its related to the banking system with one way or another . If its about the lack of usability in ATMs , local shops then there are plenty of countries and It takes time as some countries have more priorities .
Lack of proper knowledge and information and the negative news/speculations spread all over say something as well on their stand. Some countries regard bitcoin as a scam only that is unsafe for their people and risky as well. They do not want to utilize digital currency and think they that it is a threat to their existing traditional fiat currency.