Yes, I understand that to be your point and I overall agree with it. However if all of those people tried to gain employment elsewhere there are side effects.
A friend of mine with a Ph.D. in math and a Master's degree in electrical engineering works in industry in data science. He once told me that he would not want to hire people with a Ph.D. to do non research. He said they just have a hard time fitting into an environment where most other people aren't as insightful/perceptive.
Can people with the minds/attitudes/skillset of adjuncts fit into the workplaces you mention? Even if they could would it be useful? What side effects happen to the less intelligent who also compete for such jobs.
Whatever the answers are to this it does nothing to obviate the need for better labor market regulation.
