You pay for the degree but what that entails is not for you to decide. The school, and by extension potential employers who value a degree from that school, determine what courses are required to obtain that degree.
A professor can degrade your mark for a related subject just as easily by making difficult tests or not covering material in lecture that appears on tests. The problem is that these "unrelated" courses are often not taken seriously by students, so they don't put in the effort. If they were made to understand that it is an essential part of their learning and certification, instead of as a waste of time, it would become an integral part of their studies.
As it is, most courses that are related to your field do not come into play in the actual job. By your account then, those courses should also be removed from the curriculum, and courses should only cover exactly what you'll need on the job. The problem with that is that you can't know exactly what you'll need to know on the job.