The amount of overhead there is, on top of teaching and preparing materials is exorbitant. Managing TAs can be difficult as they are students and are still developing their technical skills. Cheating and grade grubbing are par for the course, but it seems to increase quadratically in the number of students rather than linearly. I think part of this has to do with misconceptions about curving.
Revising materials is more of a milestone. As technology advances, we should be teaching more up-to-date stuff, so we typically revise what we teach and then share that with other instructors. Sometimes that takes considerable work. In some positions, the program strictly restricts what is allowed to be taught. I typically stick to the core content for about 65% of the course, and then add in my own topics for the other 35%.
Revising materials is more of a milestone. As technology advances, we should be teaching more up-to-date stuff, so we typically revise what we teach and then share that with other instructors. Sometimes that takes considerable work. In some positions, the program strictly restricts what is allowed to be taught. I typically stick to the core content for about 65% of the course, and then add in my own topics for the other 35%.