Let me ask you a question. Why,can't you just use a phone for all of that?
That's simple, people don't have the time for interactive 1 on 1 conversation anymore. It all started with the answering machine, leave a message, I'll leave a message for you.
Social media allows you to keep in touch with people without ever having to talk directly to them. Yup it takes the social out of interaction in that sense. That's where all the other nonsense on facebook comes in, people still have a need for small talk, rumors, gossip and acknowledgement. The stuff you all did when visiting or meeting people in the street before smart phones and internet.
The same reason why people like party chat, no need to actually visit with people, still the benefit of mindless chatter.