[lapsedacademic]

Three things:

1. There actually aren't many low-paid adjuncts in hot fields. The CS and Eng departments subsidize the Math department, and STEM+finance+premed+nursing subsidizes all of the humanities. A philosophy adjunct is probably doing way better ad juncting than they would off on their own. And the instructional staff in the in-demand fields are generally well-paid.

2. The low paid (and usually not that low paid) adjuncts within in-demand departments are generally there as a retirement gig... if they wanted a stressful empire building type of job, they'd go into industry.

3. Runway. Adjuncts who aren't semi-retired have no access to capital and here's a really long lead time until an institution is regionally accredited. You can't take a dime of federal grant money, GI bill money, private scholarship money, student loan money, etc. until you're accredited.