One of a few self-inflicted things holding libertarianism back from being a serious governing party is a mistaken idea as to the magnitude of the differences between government and private solutions. The differences add up over a generation to huge improvements in civilizational progress but in the course of a year or two it's very often a real horse race. The impulse to close the EPA or other cabinet departments thus destroys a great deal of real value and turns non-ideological but frugal people away from libertarian solutions. That's a large enough demographic horrified by libertarian theoreticians to keep practical libertarians away from serious executive power.
Over time, the gains from shutting down government departments accumulate and overwhelm any transition losses but that tipping point is far beyond the horizon where prediction ends and vague guesswork takes over. This also makes non-ideological practical people uncertain and unhappy with such solutions.
This leaves the much more difficult road of competition and privatization of government functions. Rob and raid government meat inspectors and set up a private inspection regime. This is orders of magnitude more difficult than simply saying close the USDA. It also fundamentally shifts the terms of debate in a direction favorable to libertarian solutions. The existence of UPS and Fed-Ex daily demonstrate that the government is not the only organization that can deliver the mail. The libertarian solution for the post office focuses on getting rid of the government monopoly on first class mail and privatizing the post office, something that is well on its way in a piecemeal fashion. Nobody seriously advocates downing tools and just shutting the USPS down and that makes mail reform discussions much more practical.