I don't think any country has banned Bitcoin? Unless I'm mistaken? How would you ban bitcoins? It's like banning you playing a certain game. How would they do that? Countries have other things to worry about then Bitcoin I can assure you of that. People always talk about this or that being banned but where? How? Where is proof? Just naysay?
The main reason for this ban is it's really really difficult to control Bitcoin. Bitcoin transaction is anonymous so it's nearly impossible to find out the owner of any transaction. Beside countries banned Bitcoin because their technology still not developed enough to control Bitcoin and its disadvantages to prevent crime take advantage of Bitcoin to commit guilty like tax evasion, drug trafficking,....For now there are few countries legalized Bitcoin but these countries still not able to control Bitcoin totally so I think it'll take much longer to see Bitcoin legalized worldwide.
You say it's banned because it's difficult to control? Well then how you going to ban something that is difficult to control if you can't control it to begin with?