it really don't make sense.
Since there is a glut of PhD's and ABD's, the logical thing would be to see market forces drive down the price of a professor. Thus, instead of starting at 70-90k, Depts should be able to have new lines for AP's starting at say 45k.
But we don't see this. most new jobs still pay 70-90k. It should be a buyer's market and depts should be hiring lots of new people at low prices.