If anything I am surprised this took so long, may be it is because the market of cryptocurrencies was not big enough for countries to be able to pull something like this but as this market gets bigger then we will see more of this.
Going public with the announcement may have taken a long time, but it's unlikely they've only just started using it. They've probably been flying under the radar for a while. I doubt they would reveal their plans until they knew it was safe to do so.