They're also light on social interaction.

Compare:

    - Sending a post about your holiday experience to Facebook, vs.
    - Calling a friend, engaging in small-talk about your holiday experience and how they've been lately.

Sure, you won't be able to tell all your 1276 "friends" about your holidays, but the people you do talk to will actually be/become your friends. It's quantity vs quality. Personally I've decided that it's more important to me to have a few dozen really good friends in my life, instead of hundreds of people that passively take part in my life, thinking they know me, never really interacting with me in any meaningful way.

> Personally I've decided that it's more important to me to have a few dozen really good friends in my life, instead of hundreds of people that passively take part in my life

That's a false choice, though; while I don't use FB, everyone I know who does still keep a few good friends that they meet and talk to regularly. You and I could be scrolling our FB feeds right now, instead of reading HN, without taking time from our existing friendships.

    >  They're also light on social interaction.
    > Calling a friend, engaging in small-talk

Do you see the irony here? The small-talk you're describing in a Facebook post is just as socially-anemic as the small-talk you'd have over the phone.

If I want a deep conversation with somebody, I can message them on... FB messenger or something. Again, a form of communication easier to initiate than a phone call that they might not be able to pick up.

I don't see the irony. How is it "socially-anemic"? It is in my opinion obviously much more social to talk to somebody on the phone than to post something on Facebook. Even 1-to-1 chat as you mention is much more social (but loses an insane amount of nuance and emotion), but still much less so than a phone call (but I also chat of course).

Or do you consider everything that is not face-to-face "socially-anemic"? Are you saying that conversations via chat are deeper than on the phone?

With a Facebook post one is essentially just dumping a complete story on the masses for them to consume. It's not personalized and people cannot interact by asking questions in between, or by adding their own stories ("Oh, I loved that part of the movie! Did you also think it has a deeper meaning to it?", essentially steering the conversation into another direction), or show you that they don't want to hear about something, for example.