why bitcoin is still illegal in many countries of world

Is there any solid reason behind this ??/
Where are bitcoins illegal? China?
Try this:
http://bitlegal.io/There is a map in that website, which classifies the legality of Bitcoin by country. But remember that it is not the latest one. For example, although the situation in the US is given as "Permissive", some of the states (such as New York) are actually very hostile to Bitcoin.