Your question seems to telegraph the expected answer: the teaching is focused on recitals and advancing through graded methods. That kind of teaching isn't concerned with understanding why things happen in music.
EDIT
I wasn't going to add this initially, but there seems to be a lot of interest (disagreement) on this topic of transposing.
Recently I started working on Bach's Two Part Invention in C Minor and I simply did not want to memorize it. I've done that before with other music, and eventually I forget the stuff.
I decided to take most of the expository material and break it up into two beat units which I then practiced by sequencing the stuff up and down by step. I also inverted the parts between the hands. I made myself a sort of shorthand score of what I was doing, like this...
...the double notes at the end of phrases are supposed to show the continuation by sequence up/down. Fingerings above/below are RH/LH depending on how the hands invert. I don't expect anyone else to read this, but I think the basic idea should be clear enough.
Now I've moved on to playing each hands separately, but I play it in various keys. The music itself modulated up a fifth so you can just repeat the exposition and keep going around the circle of fifths. After working through a few keys and getting used to the changing "topographical" feel it seems I can play it in any key comfortably without practice.
I'm not done with the piece yet, and certainly this take more time than just memorizing it in C, but I definitely feel like I'm learn much, much more this way. My hands move more freely and I better understand the actual tonal content of the music.
At the very least, you aren't the only person that thinks transposing is a useful study method.