When I was in high school I took math courses. I also took a course in physics.
The math courses were all taught by the math teachers. To attend those classes, you needed to go to the math wing of the school. You also needed to have a textbook devoted to that year’s math topic.
Meanwhile, the physics course was taught by the physics teacher, who hung out with the other science teachers, in the science wing of the building — which happened to not be very close to the math wing.
There was a textbook for physics, with lots of cool pictures, examples, and some very cool mathematical equations. This textbook did not in any way refer to the math textbook. In fact, reading just the physics textbook you wouldn’t have had a clue that there was even such a thing as a math textbook.
The math textbooks took the same attitude toward physics — in fact about all other non-math subjects. Those courses simply did not exist, as far as math textbooks were concerned.
Different textbooks, different teachers, even different rooms.
Does it strike you that there is something wrong with this picture?