Status and autonomy. Even an adjunct professor still gets addressed with a honorific. You rarely have anyone yell at you or look over your shoulder as you work. And, as a friend who has a TT job at a Canadian University recently observed, it is generally the adjuncts who most adopt the professorial look: sweaters, jackets with elbow patches, horn-rimmed glasses.

So long as these things are enticing to enough people, supply will outstrip demand and wages will fall.