The professors still choose the textbook. They dictate what the student needs to buy (or rent or acquire through other means). That part of the equation hasn't

The professors still choose the textbook. They dictate what the student needs to buy (or rent or acquire through other means). That part of the equation hasn't changed in decades, as far as I am aware. But they're entirely disconnected from the financial burden that they place on their students. There are certainly some teachers who will care more about the financial cost than the "ease of use" (for lack of a better phrase). But often if you can offer an easier package, meaning pre-made content for use in lectures, etc. then they'll pick the more expensive book if it makes their life easier. So I could offer a simple book that retails for $50, but the prof will choose the one that costs 3x that if they don't have to make their own tests and handouts. Regarding your question about what happens if a prof doesn't like a chapter, we're starting to see decent growth in customized books. So for instance, for one class they might only want 3 chapters from one book and 4 from another. This is similar to course packs that have been around forever, but created by the publisher. Publishers love it because it means the "book" is custom for the course and you can't easily just buy/rent a used version. These are often sold much cheaper because the publisher is guaranteed 100% sell-through for a course.