Other possibilities that might be factors include hormones (could "settling down" be something we're programmed for?), maturity (maybe maturity makes people less interesting, and thus makes it hard for them to make friends? I have toned my personality down over the years)
What are we left with in the post university world? To some degree, we simply look for people who will (to borrow someone's words) simply tolerate us. Work friends tend to be (but do not *always* remain) a slightly more beefy version of acquaintences, more based on nonspecific need for companionship than common viewpoints/interests/etc. Sometimes this even ends up being hanging out with people one doesn't really like (as some people I knew in Columbus admittedly do). I suppose, to complete the discussion by touching on something klari said, I have immersed myself in a pre-graduation life in the hopes to make new friends. Has it worked? I don't really know. Sometimes frustratingly not, and sometimes a bit. I think there is a bit of a mismatch (a third of a generation), and I am admittedly a bit less likable (and less social) than I once was. I never am sure if I'll keep trying, but maybe. I keep hoping to find love, there or elsewhere, but I'm reallllly picky.