Not sure why you think a pannier "completes the package". Go to a college campus - no one is carrying around a pannier. If you leave it on the bike it would get stolen, if you take it with you it's a total pain to carry around all day - and no one is doing that.

College students use bikes for transportation. They don't like taking stuff on and off of it, and if you leave stuff on it it tends to get stolen (like my friend had a wired speedometer stolen - who even steals that? it's useless without the wire part). But that's what happens, so college students tend strongly to leave their bikes bare bones.