Because there are overwhelmingly more tankies than nazis on Lemmy. Most of the rightwingers moved to nostr or whatever after exploding-heads was defederated everywhere and eventually closed down. The Nazis that are left get heavily downvoted, reported and banned pretty quickly. Or are still on/back to reddit. Not saying they aren't here but they are a LOT less vocal and represented than the ultra-left crowd from hexbear and lemmygrad.

The Fediverse in general is pretty much on the left of the political spectrum. Show me one "conservative" community that is active and where posts aren't all negative