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 .
I agree about your statement, i heard that some of country like Alegeria are now passing a law to ban using Bitcoin this 2018? probably because there is no bank regulating the
BTC?
Hence, the number of countries which you can use bitcoin are higher than not, it only depict that Bitcoin have their use on digital world and each country.