Not teaching the Why is such a sin!
I didn't understand calculus properly at all until I read Steven Strogatz' brilliant book Inifinte Powers, which not only explained the why but the history of why. 10/10 book for me.
Modern education is grounded in a different worldview than the classical liberal arts[0]. The classical liberal arts are so-called because they are freed from the burden of having to be practical or economic in nature (which is not to say they could not or did not incidentally have practical application), intended to produce a free man. Here, too, by "free" we mean free to be good, that is, more fully human, not what we mean by freedom today as doing whatever you happen to feel like doing, a recipe for enslavement, misery, and despair, and therefore directly opposed to the good and to becoming more human.
Opposed to the liberal arts were the illiberal or servile arts. These are necessary and good, of course, but necessarily inferior to the liberal arts because their end is not truth or formation; they are instead practical, concerned with effecting some kind of economic end. The point here is not to disparage, but to understand how all of these are related and ranked according to a "for the sake of" relation. A human being doesn't exist to eat, he eats to exist, for instance.
Modern education is very much oriented toward the servile arts, and what passes for the liberal arts today is anything but the classical notion.
The point is that modern education is less interested in leading to understanding, realizing virtuous habits, and leading to freedom, and more interested in churning out workers. Workers don't ask "why" (though we can agree that those who do can, guided by prudence, contribute more economically). Indeed, that is perhaps the key difference between classical science and modern science: the emphasis of the former is truth, while that of the latter is control of nature. Of course, it isn't that you must choose absolutely between understanding and effectiveness, and the classical tradition does not claim either that study precludes work. Study often requires work, for sake of preparing the way for truth. Rather, it is that the end of the modern educational tradition is different from that of classical education, and this end determines the form of the pedagogical methodology. It is a difference in anthropology, of the vision of man.
All men work, but what do they work for? Do they work for work's sake, or perhaps to make money to satiate their base appetites (modern view)? Or do they work in order to be free to pursue higher ends[1]?
https://www.stevenstrogatz.com/books/infinite-powers