Well I don’t, thus keep in mind that I may be summarizing here the reasons that others do incorrectly &/or unfairly, but from what I understand people are saying:
(1) often when people get extremely argumentative (aka bat shit insane crazy trolling) it is from there. Who wants to talk to someone who is rude, condescending, and doesn’t listen in the slightest to your POV before loudly proclaiming how very wrong you are, even while using logical fallacies (such as strawman) as they do so?:-P Counterpoint: that can happen on any sufficiently large instance e.g. lemmy.world too? Though it does seem to happen more often on lemmy.ml for whatever reason.
(2) it may be relevant (tbh I’m not entirely sure how though?) that it leans fairly hardcore to what many people e.g. in the USA would consider an extreme leftist viewpoint, as in so far to the left that it may even become uncomfortable to someone living in a society that leans more rightwards even if the person in it considers themselves an “extreme leftist” in relation to that center point. Along these lines, are “memes” merely political propaganda that happens to be drawn in a cartoonish form? (Though this is an argument pertaining to merely a community, not an entire instance.)