Government could, would, and already to some extent does attempt to regulate it, but it's intentionally designed to be resistant to effective regulation. This is part of its appeal: because of this "feature", it can be used as the Paypal of drug trafficking, weapons trafficking, murder-for-hire, and other such markets that the evil governments of the world try to stamp out because all governments are run by jealous losers who want to oppress the Ubermensch. After all, the free market would work just fine for murder-for-hire markets because I could just hire a hitman to kill you, too, and then we could trade the hitman contracts with each other so that we'd both live instead of both dying, and we'd be motivated to do that because neither of us wants to die. And if you can't afford to hire a counter-hitman well then you're a loser and you deserve to die anyway. Anyone who disagrees with this is obviously a lazy bastard who doesn't understand the wise economic philosophy of Atlas Shrugged.
Bitcoin is also intentionally designed to have its own built-in and unmodifiable monetary policy separate from any government or regulating body. This monetary policy is of course built on perpetual deflation, because making it so that savers' money grows by simply hoarding it is the best way to ensure they will be motivated to make the risky investments necessary for long-term economic growth. If you disagree with this, you're obviously okay with the government stealing everyone's money with inflation, and you're also a worthless lazy bastard who's probably in debt and on the government dole.
Bitcoin is awesome.