At least in my field, there’s something of a self-perpetuating cycle. I’ve got 30+ years experience in law, solid scholarship (14 law rev. articles, one cited by the U.S. Supremes and 3/4 of the Circuit courts), etc.. Never been able to land a law teaching post. From what I see, the vast majority of law schools regard as a minimum that your degree come from the highest-ranked schools — as in good grades at the top 5, or top of the class at the top 15. I went to a top-tier school but not top 15. I’ve known attorneys from Yale and Harvard and in a courtroom I’d have them for lunch.

And teaching law is regarded as a separate career path from actually doing what you want to teach, so it’s preferrable that you get a clerking job for a judge, and then apply to teach. Actually experience in the skills you are to teach is largely irrelevant.

I rather suspect that a medical school would laugh at an MD who applied to teach surgery, and admitted that he had never performed a surgery, but he had a nice degree and had spent a year or two watching surgeons at work (the equivalent of a clerkship).

There’s also an interesting monopoly in this field. In almost all states, you can only take the bar exam if you (1) earned a JD and (2) it came from a school accredited by ABA. Understand, ABA is a purely private organization. The vast majority of attorneys don’t belong. Its accreditation standards have been controversial, extending down to size of library, what percent of faculty have tenure, etc.. I’m hard put to think of another field where a government-issue license is dependent upon a degree from an institution that meets a private, voluntary, membership organization’s approval.