You're oversimplifying (and so was I, to be totally fair). The Reddit exodus has lots of reasons. I think it has more to do with one's thoughts on corporatization and technocultural knowledge which does correlate with left-leaning politics. I'm sure there are many who are just sick of platforms giving Trumpists tacit approval (I think this is the primary driver for people leaving twitter) but that Venn diagram is not a perfect circle.
.ml has tankies, and there's plenty of fair criticism to direct at Dessalines and the mod team for generally cultivating a culture of knee-jerk anti-Western thought (and the inverse, more importantly) but it's not "closer to fascism" because it leans authoritarian and drapes itself in USSR/CCP aesthetic. But it's mostly a FOSS instance with well-deserved bashing of US imperialism and state-sponsored terrorism.
Anarchism isn't the only way to be a leftist.