I'm wondering this because is such a real threat to bank system and we all know how banks and governments are tightly linked !
BTC could make people more autonomous, self-resilient, being their own bank. You can use it like cash, making your transaction almost untraceable (or untraceable using e.g. monero or dash or laundry systems) : this is governments worst nightmare, isn't it ?
Governments can't totally make bitcoin illegal worldwide because of some of them are actually infavor in using it and they truly accept the concept of cryptocurrency. They cannot make the bitcoin illegal maube because they are having a plan on how to put taxes in it or rather control the regulation or system of bitcoin. On the other hand, another reason is, since some of the people started involving in here, governments doesn't know how to do with the money that bitcoiners have if ever they will really ban and make it illegal.