The Libertarian Party is the largest political organization in the United States today advocating libertarian positions. There is a difference between being a Libertarian and being a libertarian. Many politicians and members of the public hold libertarian-leaning views on some issues. But not all of them are members of the Libertarian party. Sometimes a Capital-L Libertarian will become a small-l Libertarian, as when Ron Paul ran as a Libertarian candidate for 1988, before returning to the Republican-fold. Gary Johnson, who held office as a Republican when he was governor of New Mexico, ran as the Libertarian Party candidate for President in 2012.
So while the philosophy of libertarianism might be a popular philosophy, how is the Libertarian Party doing as a political entity? According to the Libertarian Party's own records, listed here:
http://www.lp.org/candidates/elected-officials
There are 154 elected Libertarian officials in the United States. Of these, 38 are in partisan offices, and 116 are in non-partisan offices. The Libertarians in non-partisan offices are people who have registered to vote as Libertarians, but did not have that listed on the ballot when they ran.
And what type of offices are they in? The great majority seem to be City Councilpeople, or serving on school boards, library boards, or other such utilitarian boards and councils. There are a few mayors in there, although none of large towns or cities. I can not find a single legislator, even at the state level, on the list. But perhaps this is just a slow year for them? The Libertarian Party also has a page listing its history:
http://www.lp.org/our-history
In its forty-year history, it has elected some candidates to legislative office, but they seem to be mostly in a few states with small legislative districts, such as New Hampshire or Alaska. Beyond that, while it has gained many votes in races legislative or presidential, it has managed to win very few elections.
Since the Libertarian Party is the party that overall believes that people are responsible for themselves, and will make the proper choice when given all the alternatives, why have Libertarian candidates historically done so poorly? While it might seem at first that the duopoly of the major parties is a good answer, this is not a very good philosophical answer, since the restraint of the monopoly power of large organizations is against libertarian (and Libertarian) philosophy. Also, in practical terms, Libertarians are frequently on the ballot in every, or almost every, state. So why can't they get elected? Why is the party that believes that the free market decides things the most efficiently, so poor at selling its product in the marketplace of ideas?
I think it is a fair question to ask: if libertarian ideas are popular, which they often are, why aren't Libertarian candidates more successful?