I have been a Teacher. A lot of what educationists want from those who prepare students for their classes (in the previous year, for instance), is to be able to efficiently perform mechanical tasks.
But kids today (kids, man!) want a succinct rationale for anything that doesn't strike them as valuable. So I was at pains to try to deliver this, though it took time away from other teaching activities.
A drawback was that many kids didn't have the patience to sit through these explanations. ('Is this going to be on the test?'). To extend moral, the less teachers try to justify elements of the curriculum, the less kids are going to have sit through these explanations, and the less able they are to look at their material at a little greater depth, and the less they can participate in their own learning.
Actually, just giving kids shortcuts to get the superficial skills the teachers in the next course want, is easy for a teacher. It's easier to emphasize "I before E, except after ..." than to take just a second to mention that the spellings often come from words descended from French vs. words descended from Germanic languages, including Anglo-Saxon. Unfortunately, kids are left with the impression that spelling is totally arbitrary. There's just enough truth to that belief to make it dangerous.
Once in a while, there are a large number of interesting and lovable kids in a particular class, for a teacher to try to go the second mile, and teach his or her subject in a little more depth. And often, strong slap-back will discourage this teacher from any approach but the most utilitarian one. And they have effectively destroyed a teacher.