That’s not what happened, actually. Hexbear, for example, wasn’t federated with anyone for years until it started federating, and servers like Lemmy.world defederated before being federated. Lemmygrad.ml is fairly broadly federated, but gives the illusion of being widely defederated because Lemmy.world also defederated from them, as Lemmy.world admins are anti-Marxist (just read the reasons they gave for defederation).

They aren’t any more or less propaganda than other instances, they are different in alignment, ie Hex is Anarchist/Marxist (general) and Lemmygrad is Marxist-Leninist.