Anecdata, but I'm a typical lurker. If I don't have something to contribute to a discussion, I stay silent. I think that goes for a lot of people.
There's also the commitment angle - if you engage in a discussion, you're typically committed to follow up on the responses you get. That can be more of a time/attention commitment than people are interested in, and with the growing toxicity of online discourse a lot of people don't want to put themselves out there to begin with.
There's also your attention surface. I typically read threads/posts from a variety of communities, but might prefer to reply only on some, and lurk on the others. I'm sure this is true for a lot of people, from anecdotes I've heard.
Yep. If it's about programming, game design, board games, video games, writing, I'll feel confident I have something to say and/or want to contribute. But I also read discussion about music composition, hiking, art, diy, history, philosophy, etc, and I would almost never post in those subjects (at least not at this point in time), as those aren't my focus, just other subjects I'm curious about.
"Commitment" to a discussion is optional. It's perfectly reasonable to give your point of view, and come back a few days later to see if there were any interesting replies.
Depends on the forum. HN emphasises that, by not notifying users that they had replies. Reddit on the other hand colours your mailbox in red so you're aware of replies without actively seeking them.
I don't know which foster the best quality discussions, but I feel the HN way is a bit impersonal.
A trick I finally hit on for Reddit a couple of years ago was that when I start feeling a discussion does not feel fun or interesting anymore, I look away while I click on the inbox icon.
When I don't see the replies, they're easy to ignore.
At some point (I have no idea when), Reddit also added a "disable inbox replies" button to comments, so that you can prevent notifications on a comment by comment basis.
I have no idea. Perhaps they want to avoid discussions form derailing? Reddit routinely has long sub-threads, but they're hidden behind a link by default.
