That's something I have only realized recently despite it being kind of obvious: on old phpBB flat forums (which I personally do not regret as much as other do) you were often browsing by "recent messages" or "active discussion"

On reddit, when you do back and forth with someone for a day or two, quickly no one else reads it or partakes in it.

It would not be a huge difficulty I think to order posts and comments by "active discussion" and would greatly increase the ability to have in-depth discussions. Is there a reddit alternative that proposes that feature?