Governments cannot stop Bitcoin on a global scale for the same reason they cannot stop Internet on a global scale.
There is no cost-effective way to destroy a well-designed decentralized technology/protocol, plus it would require co-operation of most countries to destroy it.
Did I not demonstrate in a back-of-the-napkin way that it is out of reach of the NSA ($3-4 billion & deploying 500 megawatt within 6-7 months)? If the NSA cannot do it, no government can.
Trivial? Let's assume attacking the Bitcoin network would be a project falling in the hands of the most well-funded Chinese government agency: the military. (It would not, but let's assume it). This represents about 3-4% of their annual budget (~$100B), which is not quite insignificant.
There is no cost-effective way to destroy a well-designed decentralized technology/protocol, plus it would require co-operation of most countries to destroy it.