It seems like you're not even allowed to ask this question apparently. It's a combination of a large pre-existing far left base and the more center-left Reddit refugees I think. Lemmy's creators, as well as some big "older" instances like Lemmygrad and Hexbear are all communists. As to why they moved here, I have no idea. Maybe to have a separate space without an overwhelming amount of people with other opinions like they'd face on Reddit? Maybe because they hate corporations and thus don't want to deal with them? Idk.