Ultimately, I think it's a convenient excuse to cover for how truly difficult it is to teach people important things.

The adult mostly doesn't actually remember the specific logical and/or experiential steps that contributed to whatever understanding they now have. The events are too disconnected in time, and too large in quantity to really parse that way. You need that background info to teach well, though, otherwise you can't handle questions, you can't explain, etc, which are all genuinely important parts of teaching.

So, it's easier to just handwave the problem away and focus on going to work, whatever is for dinner tonight, what's going on in the neighborhood, cleaning the house, etc etc etc, and leave the teaching to the ostensibly qualified people.

If you want to attempt to do things differently, when you learn something life-lessony, remember that to teach it to a teenager someday, it's not good enough to have just learned the thing. You're also going to have to be able to offer a decent-enough explanation and answer any questions.