There's an interesting discontinuity here: - he's got a full workload (not a universal amongst adjuncts) and so the guy's skills are clearly in demand - he's taking home peanuts - students are paying a lot more in tuition than they ever did In this, as in so many areas of business, the consumer (the student in this case) might wonder where all the money is going.
Different markets. Demand for the jobs is high, and supply is low. This keeps pay low. Compare to tuition. Demand has been increasing over the last decade, and supply has remained relatively fixed or grown slowly. As more students seek to acquire trash art history degrees, price has risen to match the demand.
Most universities aren't for profit institutions churning out dividends for shareholders, so it's gotta be going somewhere internal to the schools.
I'm honestly a bit mystified.