I met my wife at a friend's birthday party, so I'll vouch for that. But there's a difference between <pool of strangers whom I might like to meet> and <pool of strangers I want to life updates from>. I'd venture that for most people most of the time, we just don't care much about the latter[1], which is I think the OP's point.

[1] One time when we may care very much is when we're actively looking for a relationship. I've found that my interest in social networks is highly correlated with those times...