Because it is uncontrolled.
Leftist think that if they can't ban you or control your money then you should be considered as far right, neo-nazi and literally Hitler. In leftist media you can pretty often see how they replace "free speach" with "hate speach".
That's how modern and progressive social trends look like.

Because during the early years of the Obama presidency, "Libertarianism," which had been historically "liberal," was redefined as "right wing."

This was a way of consolidating "liberal thought" and not allowing any deviations from the orthodox view.

bitcoin has nothing to do with "right-wing" extremism,

that would mean bitcoin would care for someones rights,

its more like private people trying to enrich themselves.

people that created it care mainly for their own rights.