What if they created Bitcoin?
We've all read about the CIA running drugs to raise cash for black ops... why not take it a step further and create your own currency?
My personal theory is it was an intel agency, or a criminal group.
Keep in mind Truecrypt was also written by criminals: https://magazine.atavist.com/he-always-had-a-dark-side
Currently there is no power to be gained in wiping out bitcoin when half of the constituents have never even heard of it. Never mind the cost.
I would assume the only reason we haven't done it has nothing to do with the cost, its simply that bitcoin is just not interesting enough to them (yet). I can't imagine that some USGOV and probably >1 non-us-gov have plans already and could rapidly build out an ASIC farm, if asked to do so (and funded, of course).
China's legal system already contains provisions which could be summarized as "all your data belongs to us".