My trajectory from politically ignorant libertarian to C-Span liberal to theory-reading MLM proponent went through Vaush. There are a few theory-reading leftists in his community -- sustained mostly by Bakunin, Kropotkin, and Chomsky -- but he has difficulty engaging with even those. Any time a leftist comes on with theory-informed opinions, it becomes clear Vaush is woefully out of his depth. So while parasocial affirmation is the cited reason, my guess would be that hosting discussions with anyone more than slightly further left than Vaush is damaging to the brand, and does the most to unravel the grift by way of contrast.