China has not banned cryptocurrency. They just banned ICO and exchanges. Peer to Peer trading is still available and actually quite popular in China. I don't think there is an effective way for government to ban bitcoin anyway.
Right, government cant ban bitcoin easily because they need this technology. Government may regulate bitcoin but for them get some taxes, government will find ways just to control bitcoin that can never happen.
government thinks that the bitcoins i s a threat into them because it can be a start of a rebellion for some of theur perspective because people can now have a freedom in currency so whats next is freedom into everything. However, bitcoin is strong enough to withstand that banning in some countries and managed to stay on the top.