“Because they are a small but steady drain on votes”
Which baldly contradicts your assertion that they’re irrelevant.
The title of the article says it best:
“Practically Irrelevant”
There are many ways to measure relevance. Intellectual relevance is, in my mind, the most important measure. And by that measure, again, to my way of thinking, libertarians have rendered themselves (they did it to themselves) completely irrelevant.
Another measure is electorally. By that measure they are “practically irrelevant”. The goal of all criticism of libertarians (and any other 3rd party poseurs, in my mind) is to ridicule them into a state of electoral effectiveness as asymptotically close to 0% as possible.