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?
An average post on Mastodon/X/Bluesky/Threads is "this is what I encounter" or "this is what I believe". Those kinds of posts don't specifically ask for a response. You can respond to it, but it doesn't require one.
That's not how you communicate on Lemmy or Reddit.
That's the difference.
Each platform has its own usages.
So to compare and say "well platform Y is more social, because there's more interaction than on platform 2" is a bit weird.
You wouldn't compare a letter with a message board on a town plaza either. Both can be used to communicate, but they're not comparable to each other.
Or in another way:
On Mastodon or Nostr, when you post something only a small subsection of the userbase actually sees it (only those who follow you, those that follow any of the hashtags that you used, or those that check the full firehose).
On Lemmy the entire community you posted it to can see your post.
Obviously you can get more response on Lemmy! More people get to see it.