Problem is, a certain proportion of all pilots and engineers progress onto other things, whether it's instructors, test pilots / engineers, authors of textbooks, etc. etc.
So, it's an inevitable fact of life that everybody needs educating a bit beyond what they're expected to start out needing, so that they've got the ability to progress beyond.
Another way to look at it, is that you teach more than they'll need, and hope the most important core of knowledge remains.
Yet another way to look at it, is that you never know when that obscure bit of knowledge you never thought you'd need will help you to extract yourself from the mire.
G