It's definitely not a ghost town. It's just not a treadmill. It's hard to have a conversation on hacker news because (1) articles cycle through quickly and (2) you don't get reply notifications. Lobsters is a bit more human scale IMO.
I don't feel compelled to read/reply to every message, there's zero sense of urgency, and this is perfect for something you do in your free/idle time.
More importantly, every now and then something you write blows up and gets a disproportionate amount of attention from others. On websites with notifications, or on mailing lists, this gets distracting and disturbing. On HN, I'm happy to find out I've had my 5 minutes of fame the next day.