Firstly, which government? It's not like all the governments of this world get along and agree on everything, particularly when it comes to money. And they can't all be in control it. Which country or union were you thinking would be in charge if it could happen?
Secondly, even if there were a single government that managed to take control of Bitcoin, which is unlikely, the open source code means everyone who doesn't want a government in control could fork away and start a new coin if Bitcoin were ever compromised in such a fashion. This is merely code on a computer or other device. It's not something a government could control even if they wanted to, because anyone can choose to run different code.
The only thing governments can control are the exchanges, payment processors, merchants and other third parties that potentially hold customer funds. Regulators and lawmakers can do whatever they like with those as long as the businesses are within their jurisdiction. But the network itself is beyond their control. They'd have to put a gun to the head of every node operator in the world, which would be somewhat time consuming to coordinate and would probably involve a lot of paperwork.
