I'm not a big reddit user, but I don't see how people keep up with the massive sprawl of the comment sections. I mean once you click into a story on Reddit (or HN, LN, etc), it seems like a pretty standard "threaded" affair which makes finding the latest bits of the conversation hard. And the nature of reddit/HN/LN etc make it hard for new topics to get traction, many people may never see new topics if the most popular ones float to the top.