We might be able to answer the question better if you named the "other platforms" you're referring to. It doesn't seem like an unusual amount compared to, for instance, how much communist/transgender content Reddit had back when Reddit wasn't as evil as it is now. (Who knows what Reddit's like now. I haven't been back since the two-day boycott over the API pricing.)
All that said, some of the communist content here is tankies. (That is, authoritarian communists who spout CCP or other authoritarian communist regimes' propaganda.) Some of the Lemmy instances (like latte.isnot.coffe and lemmy.ml) are run by tankies.
That said, a lot of the communist content here is grass-roots anarcho-communist advocacy by people like me who ideologically lean that way.