Place libertarianism here.
If I can offer an uneducated answer: the reason nations don’t “do” libertarianism is because politicians are dis-incentivized from doing so, as it puts their wealth/power/status in jeopardy. Small/no government means less/no livelihood for those in positions of power; their whole socio-economic circle disappears, and it’s rather unreasonable to expect ethical behavior from a politician.
But not only are politicians dis-incentivized towards libertarianism, they are also have the means to ignore it*. Since politicians are the ones in control of the sanctioned use of force, they can structure the political environment as they see fit. They can essentially dictate the terms of their employment. This is a semi-fancy rephrasing of “politicians have guns so they can do what they want.”
From Woods:
For some reason, the finger-waggers at Salon think they’ve got us stumped with this one: “If your approach is so great, why hasn’t any country in the world ever tried it?”
So this is the unanswerable question? What’s supposed to be so hard about it? Ninety percent of what libertarians write about answers it at least implicitly.
Let’s reword the question slightly, in order to draw out the answer. You’ll note that when stated correctly, the question contains an implicit non sequitur.
* This point is so important that I bolded, underlined, and italicized it. I can be incentivized to have $1 million in my savings account but it doesn’t mean much if I don’t have the means to fulfill or even reasonably pursue that incentive.
Medieval Iceland image stolen from Wikipedia.