The answer is quite simple really, why would governments allow something like Bitcoin flourish on which they don't have any control over. The governments make anything illegal that they cant control or have any power over. And if you are waiting for the governments to make bitcoin legal than you will have to wait a long time.
In fact, the government does not necessarily need to legalize bitcoin itself, in the case of legalization, many internal economic problems may arise. I think the government is much more profitable to create its national crypto currency and this would be logical and modern.