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 ?
I think they do not make bitcoin illegal worldwide because they still hoping that someday they are the one who control it. Actually we all know that government wanted only to put a tax on it and that is the start of everything.