Some qualification: It's small enough that each board has a global chrono view of posts, same with replies on posts. You can reply back and forth and still understand what's going on despite the other noise.

Given that there’s basically no way to interact besides posting or replying, I’m willing to bet most of that traffic is just lurkers. And another large chunk of that traffic probably congregates on boards like /a/ and /g/.

Some boards are incredibly slow given the popularity of the site as a whole, threads on boards like /n/ can stay up for weeks with barely any replies.