The reason libertarianism is a political failure is because the main motivation for the “movement” is “I want what I want, and I want everyone to leave me alone”.
Political movements are built by selfless true believers who are willing to sacrifice to see it through. If the only reason you’re part of a movement is self-interest, the minute you face difficult opposition that requires much work to over come, the inconvenience of it offsets what you hoped to gain and you give up.
And not only that, but the entire libertarian philosophy claims that self-interest by definition supersedes any moral, societal, or ethical standards. See, for instance, their stance on “consensual crime” or their willingness to support abortion as long as no one’s “liberty” is infringed upon.