Having tried all three, its a stark difference in how much more social Lemmy is comparatively. Its not even close. Almost all posts I've encountered on lemmy have interaction; whereas, more often than not, posts on the other two platforms have no interaction. Wonder what the driving factor is behind this difference?
Honestly, I think is the whole ”First Post” mindset.
When you post a reply on Mastodon, it is more intimate, the only people who see it are the original tooter and anyone who actively seeks more commentary. It is a dialogue between two people, or multiple dialogues between one person and many others.
Lemmy is more like a forum, where everyone can see all comments, right underneath the original post. It is more like an open-table discussion.
It is not that Lemmy is more social, it is just less personal.