I have kids 21 and 24 so probably the ages of some of the posters on this thread. This is an interesting topic, to me, because I've thought about this very thing.
We're also very "socially active." But being socially active and involved in all kinds of organizations and groups doesn't necessarily mean you have friends. The kind of friends that drop by the house, that you call at the last minute to go grab a pizza, etc. You can be very socially active and have close friends, the kind that help you move or build something for your kids but others it's just acquaintances.
We have a LOT of acquaintances but are bad at keeping in touch with good friends and a couple months ago I started working on fixing that. Regularly calling the couples we really enjoy. Some of them are parents we met through our kids sports and other activities and some from groups we belong to (yacht club, etc).
I think it is VERY easy to just get so busy going and doing things and be involved in almost too much so that you don't really get to know people well and become close to them.
I remember when I was growing up that on Saturday and Sunday afternoons you couldn't walk through our house (and we had a big house) cause I swear everyone in 7 counties stopped by to visit with my folks and whoever else was there.
My parents loved to have people over and obviously people enjoyed being there.