I don't see any reason why would the US government have to build Bitcoin and Darknet to release it to the public, that would potentially destroy their current financial system, then have main stream media, bankster, Institutional investors comment pessimistic things, and would have to take down darknet due to large criminal activity.
Bitcoin cannot risk official government currencies, as nothing backs it up, so most cryptocurrencies collapse or remain with low value. The US government maintains a relatively high currency value so that people can continue to mine it and provide free computing power for NASA. The only expense of the United States government is to occasionally buy Bitcoin from the public if the currency starts to collapse completely. Therefore most of the other cryptocurrencies have collapsed or remained with low value.