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.
One of the big things driving interaction is that Lemmy's default comment sorting algorithm is a bit backwards to reddit's. As long as you get upvoted once, newer comments will appear at the top. So even if you participate late in a discussion, you're likely going to get responded to by other latecomers.
The fact that comments are prioritised by simple rules, an not by some sort of monolithic ALGORITHM, keeps the discussion dynamic.
It's still an algorithm.
I am inferring a difference between an algorithm that is based on simple rules, and an algorithm that is constantly being dishonestly modified for commercial, political and financial benefit.