One thing I haven't seen mentioned: 'Friends' in your teens and twenties are often really about having someone to hang around with while looking for a mate. So you won't look like a lone loser at the club, or in social situations, or so that you get to meet members of the opposite/preferred sex through the group.
Once people get married and have kids, all of that falls away, and so do the 'friends'. You don't hook up with new people, because either they want partners to ride shotgun with them while hunting for a mate, or they are set up too. What's left are people you have a real connection with, usually people you were friends with since you were kids, and those few family members you can stand being around. For many, that is a small to non-existing group. What's left is your wife and kids, and honestly? The best company there is, IMHO. And I am not worried about what I will do when the kids leave and my wife divorces me, silly me.