Why is it that adjunct faculty positions pay so little?

The adjunct model seems to be predicated on an assumption that most adjunct faculty are presumed to be employed somewhere else. It's supposed to be a win-win: the institution gets a qualified expert with current, out-of-the-ivory-tower experience; the adjunct gets a chance to scratch a teaching itch, or to work with the university. All this happens for a modest compensation – which turns out to be a bargain for the university, and a little extra pocket money for the adjunct.

I didn't read all five of the articles you linked to in your question, but I did look through three of them. They seemed to be focusing on the depressing conditions for those who are trying to make a full-time living through a collection of part-time teaching assignments. I don't think that's the way the system was ever intended to operate.

Where I teach, I'm an adjunct, and I love the perks. I get to use the campus gym, and I get access to campus library resources. I have a passion for teaching, but I don't get to do much teaching at my full-time job. The extra money hasn't made me wealthy, but it's led to a few lifestyle improvements and splurges for my family. $9,000 isn't enough to live off of, but it goes a long way when you want to renovate a kitchen, take a vacation, or help pay for a wedding.

Moreover, where I teach (a state university in the U.S.), the adjunct rates are not set by the department. The going rate is the going rate, take it or leave it.

My brother once asked me how much my adjunct job paid per hour, if I factored in prep time and grading time. I told him that I never bothered to calculate that, but it didn't matter, because I enjoyed my duties too much to give it up. I'm fortunate in that I'm not doing this for the money, so even the relatively low pay is very much appreciated. I enjoy the challenges of teaching, the chance to experiment with new pedagogies, and the chance to make an impact on the future.

Let me put it this way: Teaching two nights a week for fifteen weeks? $3,000. Staying up until midnight grading final exams? Zero extra dollars. Getting an email from a student from two years ago, telling you about how she's using stuff from your class at her new job? Priceless.

I believe the answer is simply one of supply and demand. As you mentioned in your question, there is an oversupply of those willing to teach. As the old saying goes, those who can, do. Those who can't, teach. While this saying does not represent my feelings I did find it a quite typical American perception toward the teaching profession.

Years ago I taught as an adjunct in the US. The hourly rate (just for teaching hours, forget prep, marking, etc.) was so low that I could make literally four times as much working in 'the real world.' The math was quite easy to see. They needed someone with lower skills than I had and while I could do the job, so could most others.

As you can imagine, I didn't stay in that situation long. I stopped teaching at universities and focused on the private sector. Those whom I taught alongside felt like they were lucky to have their opportunities (I clearly felt differently).

If you scan websites for teachers (e.g., the Chronicle, etc.) you can see countless posts of teachers complaining that some other teacher took their job. Sometimes it is a full time teacher who wants extra money so they pick up adjuncting at another school. This constant oversupply naturally pushes rates down.

So, why would schools pay more than they need to? Out of the goodness of their hearts? In the US, sadly, teachers are not valued. If you look at Europe or Asia, (average) teachers actually make quite a nice living because they are valued for the dual-professionals that they are (subject matter and pedogogy).

In addition to other useful comments and answers: in my context, of mathematics... : yes, only a very small fraction of "adjunct" teaching is done because of lack of expertise of "regular faculty". Examples would often be "financial math" or "actuarial math". Far more typically, adjuncts teach very low level math. Now, on one hand, while the mathematics itself is very easy, reaching the audience is non-trivial. Full of pre-existing neuroses, etc. Although the typical adjunct teaching such things has very modest mathematical ability, that is more than sufficient, and, typically, such a person's ability to "connect" to "normal" kids who're "having trouble with math" is greater than that of talented mathematicians. (Tho' not always.)

True, "The Market" observes that there are many more people able to do this than the number of jobs, so the pay is depressed. It doesn't help that there is a mythology in (academic?) mathematics that teaching itself is something anyone can do, perhaps after one has lost the "zip" to "do research". All the more ridiculous that this mythology exists among people who's teaching is awful, at every level, their whole life. Luckily, their job description emphasizes "research".

But the mythology, seemingly confirmed by The Market, marginalizes (non-specialty) adjuncts. At my current institution, none of the (non-specialty) adjuncts has a Ph.D., which further reduces their status.

And then there is the current budget squeeze on universities... Everything has to be done more efficiently, etc. Departments' supply budgets are cannibalized to pay for office staff, etc. It is crazy. Night-school classes, once paid for through separate budget lines, have been "in-loaded", so have to be covered by departments often with the same budget as before (!) So, hardly the time to think about equity for people who're willing to "work cheap".

The AAUP has long argued for better treatment of "adjunct faculty", but harsher economic times are not fertile grounds...

For that matter, often the real competition for adjuncts is grad students as Teaching Assistants, who are "more expensive" if their tuition is included in the package. Thus, at best, adjuncts have some incentive to keep their pay below that of grad students + tuition. A crazy dynamic.

It is true that the volatility of enrollments gives management incentive to find a way to avoid liability... but in the dim past there was simply consistent excess capacity, not so much a population willing to absorb that volatility!

Nowadays, upper echelons of the university almost make it against-the-rules to cushion people (other than tenured faculty) against volatility...

Not a happy situation.