I just wrote a post on Quora where I answered this question and I thought to share it on Steemit as well.
Here is my answer.
No country dares to implement it because the problem of implementing a crypto-currency is a two-fold one.
On the one hand, it is not very easy to implement a blockchain where to run your national coin. Even governments with them virtually “unlimited” resources have some difficulties with such a task.
On the other hand, this is something very risky due to the fact that blockchain technology is a quite new toy and playing with it might have quite unexpected outcomes and I’m thinking of the famous DAO here.
This is definitely a great moment for the development of our modern society and I feel that we are privileged to live in such a moment of human history.
However, there are different attempts and efforts in this direction by the governments of different states, such as Estonia of which you can read here : Estonia plans to launch est-coin
Something to keep in mind is that estcoin is not considered here as a national currency as Estonia lives inside the Eurozone. About this idea, Mario Draghi the ECB governor opposed to Estonia releasing a digital coin as the country already has its own currency which is euro
Other pioneer states that are trying to evaluate this possibility are Russia, Dubai, Venezuela and in the last days also the government of Israel announced thinking about it as you can read here Israel Government Considering National Cryptocurrency
So yes, the question makes sense as the great majority of states do not even have such possibility even in their wildest dreams but there are however some prime movers (as Porter would say ) which I already listed above.