You do memorize why's but part of arguing the why's, either to the teacher or in groups, is to add interaction with the details. It may or may not be a barrel of fun but it is, by definition, more engaging. Whether or not that's a personal case is going to be subjective but yes, most people really do like learning via more than rote memorization alone all the time in lieu of mixing it up and engaging on average.
I've definitely had classes where the teacher wasn't able to make the content interesting/engaging - it sucked either way in that case. I'm not as sure the teaching "fails" as much as is "not as good". That students zone out is no measure of a method being universally bad, that the method is single approached and almost all students zone out is a good indicator though and that's what you get with constant memorization only.
The result is that students just memorize the whys, sure you can always go beyond that and have fun in every class but that has very little to do with the teacher bringing it up, because the teachers brings that up in almost every class or at least the books does. So, that they focused on why is still rote memorization just like the focus on facts, sure facts do tell an interesting tale but if people ignore that and just memorize the facts then they aren't any fun. It is the same way with looking at "why", it is just a bunch of facts in the end and most students makes that boring.
> Sure, you can find some worst case of student and worst case of teacher where this can devolve into being no better than raw memorization
No, that is the normal case, almost everyone here did this which is why they have so horrible memories from school. You too probably did this, memorized stuff when the teacher desperately tried to get you to engage with it in more interesting ways, otherwise you wouldn't have thought it is so rare for such teaching to fail, because if you really saw all the teachers that tried you couldn't have had that opinion since you'd see all your classmates zone out and be bored and ask for rote memorization details.
I've never ever seen a schoolbook that was just a list of facts, it just isn't a thing, students still doesn't engage.