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?
Mastodon & others are microblogging (aka shitposting) platforms, while lemmy lets you ask questions in posts that will persist (not get flooded under a megaton of shitpost, hentai) and get answers.
On mastodon what's important is who you are (who you know, who you can interact with), on lemmy your post's content is more important.
On Mastodon, follow and interact with people you admire, not content.
Go to pypi look for packages you admire, find their maintainers, and get chatting with them. Coders make themselves available on mastodon. Not lemmy. Not twitter. Email is passe.
Do a survey. Look up 20 random packages you admire on pypi. What contact info do they provide? These packages must be actively maintained. Otherwise understand if dinosaurs in the past communicated thru mostly hand gestures and grunting.
Published coders are the richest resource of talent in the history of mankind.
Lemmy ... asking questions?! Is that it?
There is more to interacting and collaboration than hit and run knowledge sharing.