Keep in mind that private currencies undermine government monopolies.
As I said, small potatoes. The magnitude of bitcoin isn't enough to really concern most governments, and certainly not the ones with the resources to do what you suggest.
Bitcoin itself is immaterial. The concept of currencies outside of government control tends to make governments nervous. Remember when they took down Silk Road? Government spokespeople went on and on and on about how Bitcoin was being used to launder drug money and was a Bad Thing because there was no government oversight on it. Silk Road was what, maybe 1% of all Bitcoin traffic? But I digress...
Could it be a case of criminals in a government being behind this?
Sure. Could it be alien space monkeys trying to destabilize our currencies and use us for slaves to harvest tasty bananas? Sure, I guess
There's about as much evidence for either of those, which means there's zero evidence at all.
I generally tend to fall a little on the tinfoil-hat end of the spectrum -- but in the absence of evidence, I fall back to "Never attribute to malice that which is adequately explained by stupidity."
You're well into just claiming it could be a conspiracy, but I just don't see the need. It could be if you want to be paranoid enough. But there's nothing real to suggest it's true, which makes it just pure imagination for the moment.
Again, look at the forest here. Who benefits the most if private nongovernmental currencies come undone? Governments and corporations. Occam's Razor says, even if there was no governmental or corporate involvement in the heist, they won't bend over backwards to help the victims recover their losses, and just may be quietly cheering on the 'thieves' from the sidelines. It looks win/win for them to me.