At least some of the time the reason is the canon of that subject requires it and you either care about that subject or you don't. If it's a distribution requirement the school imposes or the student simply doesn't know yet what they enjoy studying and are still major-shopping, there isn't necessarily much a professor can do about that. It's not like cooking. Everyone has to eat. Not everyone needs to become a chemist, but if at some point you think you might want to become one, you're going to have to learn common foundational material that all chemists must know to succeed as chemists. If you end up not actually becoming a chemist, it will never be useful to you.

Or if you're pre-med, it still may never be useful to you to learn all the different ways atoms can arrange themselves into molecules unless you're going to someday do novel drug research, but medical school admissions and clinical licensing boards have not yet figured out a way to craft pre-requisites based on the specific unknowable future paths of individual applicants and they have to require everything that might be needed by any kind of doctor.