I think you're misunderstanding the challenge. Teaching first year students doesn't require Ph.D.-level knowledge, but it requires more teaching experience and skills than teaching later levels: The classes are larger; the students are less experienced at learning on their own; the students are new to the environment and less familiar with how to navigate it.

Large classes of novices are particularly sensitive to logistical and teaching errors. You make a question on a homework or exam a bit confusing, you have 400 students utterly perplexed who may not have the domain expertise to know it's the question that's broken.

At Carnegie Mellon, our teaching-track faculty generally own the large intro classes for this reason. They're the best we have at the process of teaching & education. It's the exact opposite of a side job. You want people who are deeply expert and passionate about teaching so that you don't completely botch the job, because the opportunities to botch it are huge.

If you’re representing the college, how do you know the individual you’re about to hire has sufficient knowledge to both teach the material and cover any questions on the material students may raise.

Nope. They are having problems filling positions because the market has given people a better, higher paying option.