I have no proof what so ever, this is just a conjecture: there are powerful government and private entities who profit from manipulating the current monetary system. I have to ask: is it unreasonable that state actors would try to crash Bitcoin out of self interest?
There was an article going around just the other day alleging that GCHQ were DDOSing the QuakeNet and Freenet IRC systems. Not the same, but a similar kind of thing.
One issue with this is do we even have any evidence somebody can reliably short Bitcoin at the level a government would want to? It seems hard to believe a government could do more damage to Bitcoin than just declaring that it's banned in their country, anybody using it gets {significant penalty in their country}.
So the claim is they'd be doing something like these attacks? I just struggle to believe that's the most effective way for them to deal with the problem, when the US Government coming out with "Bitcoin is illegal due to {plausible sounding terrorism story}, possession is a felony" would utterly tank it overnight.