They are not the same skill. Being able to teach and figure out how to cure cancer aren't the same. And for 95% of the classes at the undergrad level you don't even need that.
Despite your claim, I remain confident that knowing about something is a vital skill if you are going to teach that thing.
Of course, if you think that the only value students get from learning is the degree certificate, and that they therefore need only to learn the things that are on the exam, then I can understand your confusion; and can only repeat that there is no hope for you.
HINT: The top researchers in any field likely took an interest in more than just the minimum requirements of the syllabus while undergraduates; and only because they had access to people with cutting edge knowledge in their field were they enabled to become top researchers, rather than taking their degree to the wider employment market and becoming overqualified cubicle drones, selected by HR departments that insisted on a degree just to keep the number of applications down to a manageable level.