Obviously this is my opinion based off observations I’ve made, and not every user or sub in each instance falls under this generalization.

Both instances have a lot of users, and they have ideological differences, so they inevitably butt heads. Depending on who you ask, ML mainly has socialists, communists, or tankies. World seems to be more centrist leaning to the left, but it seems to be accepting of a more varied range of political opinions. Considering a lot of Lemmy users came from Reddit, I think a comparison can be drawn. My opinion is that World users have an ideology similar to most of Reddit and seem more likely to have left Reddit because they took issue with specific Reddit admin policies. On the other hand, ML users would have had an ideology that was more fringe for Reddit, and while they may have had issues with Reddit admins as well, they seem more likely to have left Reddit because their views were not well accepted among Reddit’s general population.