Some government ban bitcoin, because of they protect their own currency, that bitcoin will be becoming more popular than their currency, the other reason is their banks will ignore by their people on their country. So if they allowed bitcoin in their country they can't get tax from bitcoin. They could not control anymore if the bitcoin will indemand already, so they will do is to ban bitcoin. Not only for that reason the bitcoin is most stronger currency.
The problem with bans is that unless you solve the underlying issue people are going to keep using that which is banned, if a country is suffering hyperinflation some may decide to use bitcoin to escape this then the government realizes that and bans bitcoin but does nothing to solve the issue of hyperinflation, when the choices you have are to have enough money to eat and the chance to go to jail many people will take the risk and will prefer to keep their bitcoin and have food on their table than to die of starvation.