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 .
Yes, it is about their laws and the current status of their economy especially those countries that are currently suffering from financial problems. It affects on how they are going to manage these circumstances. I also think that they are not supporting it because they think that it might worsen their financial problems or maybe it could become a threat to their plans and success in solving their financial issues.