Short answer: He's a moderately popular drama streamer who's politics are about as left as Bernie's domestically and about as right as Reagan's in terms of foreign policy.

Long answer: He's basically First World "Leftism" incarnate. Whenever someone puts scare quotes around the word "anarchist", what they're imagining is Vaush. As such he's become sort of a totem, a caricature, a representation of everything actual communists hate about most other leftists, which is why they dedicate so much time to hating him. There seems to be this idea that if we can take him down we can destroy first-world-baby-leftism.