this is an interesting question i’ve had banging around in my mind since well before Reddit’s implosion (and Discord’s enshittification), but which seems really worth asking now.
you can’t blame Reddit and Discord or their imitators entirely for these going out of style, but they’ve sure put the dagger in a lot of remaining ones, and i kind of wonder if they’re just in an irreversible and terminal decline a la USENET. i can only name two or three i even consider checking anymore, and i’m not sure how sustainable any of those are long-term.
I have absolutely no ability to read a several-hundred page thread anymore. I think the dig/etc innovation that killed them was vote-weighting posts and comments rather than chronologically ordering them. It gives you an ordered list of things that are worth your attention. Folks inclined to read deeper than that can get a bit of a rush from finding some hidden gems and helping them rise to the top, either with new posts linking to a comment or otherwise.
I think the new way is much better.