Insofar as anarchy represents an outlook in favor of tearing down the existing structures of a civilization, then it's not surprising that a lot of lefties claim to be anarchists.
Furthermore, given that Marxian politics seem to have an inbuilt feature of continuous "revolution" essentially without end, and that it encourages people to constantly try to tear down whatever societal structures exist (even if they're post -capitalist, -democratic, -theologic) then through that particular lens of crazy, big state lefties can always claim to be anarchists.
Claiming to be an anarchist fits their narrative better than Neo-Nazi.