There's a bureaucratic reason too. Changing curricula is not fast and can take years (depending on the institution of course). My department profs actually got

There's a bureaucratic reason too. Changing curricula is not fast and can take years (depending on the institution of course). My department profs actually got in a bit of trouble with the university because they took the course that they should use for undergrad/graduate mentoring (something like a "special studies in XXX" placeholder, usually for independent or small group study that was special enough for course credit) and used it to create their own courses outside the review of approving a new course with a distinct number and credit count. The reason they did it in the first place was because if they wanted to change the curricula for the existing courses, remove course numbers, or create new ones, the bureaucracy would take 4-8 semesters to get approval and complete. By which time some of the material was obsolete. One of the profs got fired and the rest quit, eventually.