All true, but it slides by the main issue: what are all these Ph.D.'s going to do? In the post-WW2 era, when the percentage of high school graduates was going up, each professor could have several Ph.D. students go on to find jobs as professors. With no Baby Boom, and the percentage of high school graduates having flattened (which was always guaranteed to happen eventually), many fields don't have enough other options for people who get their Ph.D. In some fields, sure, there are corporate R&D centers or other places to put that to use, but in many fields, a job in academia is the only plausible place that Ph.D. students have in mind as their eventual destination, and there's just no way most of them can get a spot there.
The universities shouldn't be relying on 2/3 or 3/4 adjunct professors, but they're doing it because they can, which is because the system as designed produces way more candidates for professorships than there are positions available.
The universities shouldn't be relying on 2/3 or 3/4 adjunct professors, but they're doing it because they can, which is because the system as designed produces way more candidates for professorships than there are positions available.