Well some government in different countries banned bitcoin, because they are afraid that some people may use it for crimes and terrorism it would be a big risk from them, yet some poeple are worries about the bitcoin, asking that why it should be banned? Maybe some knew the answers and all they can do is to follow what the goverment implemented and if they dont they can be arrested. There are other reason why they banned bitcoin, i know that this not enough but you could read some articles about or search from the internet to enligtened your knowledge.