I think the confusion is that the term is used for all sorts of things like economic liberals (neo-liberal de-regulators), social liberals (into multi-culturalism and identity politics) and Ayn Randian sea-steaders and techno-utopians, which is where classical liberals often seem to end up on a diet of extreme capitalism and sociopathy?
In Europe, left libertarianism is very much a thing, as identity politics and re-distributive economic socialism often find common ground in empathy for those who are disadvantaged in different ways. The right to exploit others does not trump the right to not be exploited, unless I am badly mis-remembering John Stuart Mill?
Don't really know why, but it's what they seem to want to do.
> The term libertarianism was first used in the U.S. as a synonym for classic liberalism in May 1955 by writer Dean Russell, a colleague of Leonard Read and a classic liberal himself.
What precedes that paragraph is mainly about the French word "libertaire" which is not the French translation for "libertarian" but does shares a root with it (liberty).
Interestingly, the French Wikipedia article[0] claims that the word "libertarian" was coined specifically to distinguish classical liberals from modern liberals in the US.
In the US at least, libertarians very rarely identify with the "left" label.
Colin Ward (2004), Anarchism: A Very Short Introduction, Oxford: Oxford University Press, p. 62.
"For a century, anarchists have used the word 'libertarian' as a synonym for 'anarchist', both as a noun and an adjective. The celebrated anarchist journal Le Libertaire was founded in 1896. However, much more recently the word has been appropriated by various American free-market philosophers."
No one’s denying that it’s modern connotations hem toward the right-wing cooption that that took place in the 1950s. Their project was to dress up reactionary ideology as radicalism and was undeniably successful.