One reason I can see is the truth that transactions are highly untraceable. The governments wants to have records of their people's transactions especially when it comes to income. Digital currencies', especially Bitcoin, transactions are not governed by tax laws of any nation and that is the reason why some countries look for ways to control it. This results to traders giving up their positions thus lowering the digital currency prices like Bitcoin.
Bitcoin market cap is still insignificant in the grand scheme of things. Less than 0.1% of total population of earth is owning Bitcoin.
Do you think that governments would be control freaks to the point to scare people from potentially the best investment of our generation?
Bitcoin can be shut down only if EVERY single country unanimously would outlaw it when one or two insignificant players will ban BTC it won't cause much harm to the whole network.