Why is math so difficult to teach and learn? Because the teacher does not know what the students do not know. Teacher may not even be aware of what they themsel

Why is math so difficult to teach and learn? Because the teacher does not know what the students do not know. Teacher may not even be aware of what they themselves know and assume, therefore it is hard to share with the students what those necessary pre-requisite assumptions are. In other words something may seem obvious to me without me being fully cognizant of why it is obvious to me. However I digress, the original question was why there is so little motivating examples and motivating problems in math text-books. Maybe it is because the authors are not aware of them.