Her primary goal is to teach the students. You don't serve a novice mechanic well by asking them to build a Formula 1 racing engine from scratch on their first day in the machine shop.

She's not saying that material is not worthy of study, clearly she thinks it is because she did teach it in class previously. She just found that the material didn't provide the best platform for education in the subject relevant to the students.

EDIT: Note that the reason for changing the material was not due to the students being soft. It was because "The historical material is too painful for a music class". The point of the class was to study music, not the historical context of the lyrics, so selecting such historically charged material distracted from the actual purpose of the course.