It's not that simple for people that aren't in the same circles as HN readers. Younger generations utilize it as their primary means of keeping in touch with people. That's fine if you get along well without it. But take a step back and look at all the teenagers who grew up with never not having Facebook to keep in touch with their friends/setup events/etc. You remember how difficult the social aspect of your younger days were in school.
Facebook/Twitter/Instagram alleviate some of that for the younger generation. I've seen that in many youth that I've worked with over the years.