It is because of the criminals who use bitcoin, because of these criminals a lot of other people also lost access to that beneficial currency, the government should have to device some other procedures to stop the criminals to use it.
Criminals using bitcoin nothing other than a lousy excuse in an atempt to control the only thing they couldn't thus far - a decentralized p2p payment system,
that puts the faulty and essentially worthless fiat to knees.
The real criminals use fiat, and do their deeds in broad daylight on the open, but you dont see governments fighting them .. ask urself why.