"Most professors give lectures that aren't directly taken from the book."

If this wasn't your college experience then I think you're in the minority. If you look at a list of the top 10 most popular college majors, I'd be willing to be that the majority of classes in these majors are taught almost directly from McGraw Hill textbooks or whatever. It's not until you get into subjects that are both obscure and also in areas where the professors are likely to be intellectually curious that you start seeing more people creating their own lectures, e.g. a course on methodologies in religious studies or whatever.