I'm not saying everyone can teach equally. I'm saying most everyone can become qualified to teach. Please don't accuse me of saying teaching is easy. At the very least, a much larger subset can learn to teach than can learn to code.
This is true, but it's become a partisan issue, at least in the U.S, to talk about testing teachers in some way.
I believe a huge problem is finding a way to differentiate a good teacher from a bad teacher if you're not allowed to look at grades/some kind of standardized test. If you can take those into account, as long as a teacher comes into work on time I'm not sure how you could differentiate the good from bad.
An example I like to use is my AP Calc teacher from highschool, who had an average score of 4.7 for her students on the AP test. The average in 2012 was a 2.9 (the year I took it, it seems to be higher now, I can't say to as if they made it easier or if people got better though) [1]. In many school systems though, if your teacher has an average score below the national average, you can't do anything about it.
[1] https://www.totalregistration.net/AP-Exam-Registration-Servi...
OP's wife may place a high intrinsic value on teaching, which serves as a kind of internal subsidy. In that case you'd expect the job to pay less, because more people are being 'subsidized' by their desire to do it.
On the other hand, nobody is burning with desire to be a garbageman. Nobody is a volunteer garbageman, and garbagemen make more money than you might expect (or at least, they did when I was graduating from high school.)
There's a reason glamorous and fun jobs generally don't pay very much. It's not that complicated, and it's not sinister.
What his story underlines is that teaching young human beings about navigating life is rewarded 3x less than churing out code that fits some business objective.
The market doesn't care about people, it cares about profit. In that system, human life is only important to the degree that it helps market dynamics.