I think it is more than just being selfish and such. At least with people that have families. When younger, I spent a lot of time with friends, I was never on any instant messenger or anything like that. When I started my family, I had a lot less time. I worked 2 - 3 jobs to make sure my kids have what they need. My wife also works. Given the amount of time work requires, there is not a whole lot of time to spare. So the majority goes to spending time with my kids and getting things done around the house. That does not leave much time for outside activities. So I go on facebook to at least keep up a little. For me, I can spend 15 minutes and catch up with some of what is happening, at least a little. For me, given my busy life, something has to be put on the back burner some. SO what goes? Family, home improvement and maintenance, or time with friends? Obviously family HAS to come first. I doubt anyone would disagre with that, especially those that gripe about how parents do not teach there kids anything. Of course a person wants to keep their house in decent shape. Not just or looks but safety and a good roof. So the last is friends. So since I cant see friends as much, I can keep somewhat up to date on what they are doing. Once my kids are older, not such a big deal.
So while social media might have something to do with it, I do not think it is a cause, just an effect.