My first suspicion upon reading this was that some writer or editor observed that they weren't getting together with friends as much as they used to and spun a story with some plausible theories and anecdotes out of it.

The real answer may be as simple as they got a bit older, people they know got busy with partners, family, kids, etc. and tend not to be available on random nights and weekends.

I'm willing to believe that there are meta-trends which have caused shifts in how and how much people socialize in addition to this but I'd need to be convinced.