AP physics is much harder to learn well enough to teach than PE. I'm fairly certain that anyone in the school would have a harder time if they were told, with a week's notice, that they had to teach physics (taking AP out of the equation) as a new course, than if they were told they had to teach PE. Calculus would be harder to learn (well enough to teach) than construction class. I could teach Algebra without any major issues even though I do not have a math degree. I couldn't teach calculus even though I've taken that course far more recently than I have Algebra. Not belittling Algebra. I think it is one of the most courses taught in high school. But it is easier to get a deeper and complete understanding of, for the average person, than calculus.