Education is largely intuitive. People have been teaching since the beginning of people. So, you have a bunch of people who try to apply social science techniques to what is natural. We're all people who have been taught things--it's not like we're training monkeys.
It's like taking a class in sales. Yes, there are things to learn, but it's not that difficult a concept.
But, the kicker is that teachers' salaries increase with more classes. Colleges get paid. Teachers get paid. However, the correlation between teacher courses and performance is probably weakly correlated and probably not causal.
I'm talking specifically about theory classes, not classes that teach practical things like lesson plans and discipline techniques.
Now, I'm not 100% cynical. If teachers have a different experience, I respect that.