I loved posting on phpBB forums back in the day. Checking in every so often to see if anyone had replied to my posts. Often recognizing the same people, but also a healthy flow of new people.
Oddly... there was no such thing as push notifications and yet you could reliably count on people to check back. I guess because people were not coming from a feed or Reddit-like aggregator, they'd entered the conversation more intentionally?
No, it's probably more that a given thread was one conversation, like a GitHub issue, not a tree of comments with nested branches. Linear forum threads are great like that, posting is like joining a group of people by the vending machine, you're now in the group because you interrupted everyone else when you chimed in with your two cents, but that also means you belong there now.
Oh, and even more relevant: upvotes have zero effect on what post gets seen first! So it's not a popularity contest for the most pithy one-liner that gets upvoted to the top. You can write long-form posts and people will see them and engage on a human level.
I guess you can boil this down to "the absence of an algorithm": nothing has attempted to optimize what to put in front of their eyeballs, and so they engage with your long-form post. But when we talk about "opting out of algorithms", remember it's not just ML/AI algorithms: even Reddit/HN style upvotes are already an algorithm! It's obviously powerful enough that it has quite an effect.
Not sure why modern alternatives to phpBB, like Discourse, feel so impersonal and boring. I rarely feel the urge to check back on a Discourse thread, but that may just be me.