why do governments don't make BTC illegal worldwide ?

[sashavich04]

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 ?