That’s a good point. The reason I don’t write about it much (although it is covered in the beginner course) is because it’s very resource intensive and I simple don’t have the know-how and money/skills to produce accurate and instructive graphics/video for something like this. I do show/talk about this in class when teaching all the time, though. That’s quite rare, though, I’m somewhat of a phonetics nerd after all. The truth is that most teachers, native and non-native alike, simply don’t know enough phonetics to accurately describe (draw, explain, whatever) all the sounds. So, it’s either because it’s hard/expensive/time-consuming to produce or because the teacher doesn’t know enough to do it. Or both!