Obscurantism and leftist "intellectual" writing

Does anyone know why obscurantism is somewhat prevelant in leftist writing? Why is it more common in leftist writing? Does anyone know where this began, how it began, why it began? This happens with film critics, marxist feminists (from my small observations they seem the most guilty of employing it), and most social science groups. Oddly enough, I don’t think I’ve really come across it too often with environmentalism (not that I have read much on environmentalism). One would think the Sokal affair would have stopped this nonsese. Are there any links to articles someone can give me?