College level textbooks in USA are a total racket. The major textbooks come out with a new revision roughly annually, where the material is reorganized enough to change section and exercise numbers. The purpose is to destroy the used textbook market, as assigned reading and homework will not correspond to older revisions of the book. Then students are forced to buy new books and the publishers can make big profits.
So it's the schools that are in on it and the primary target to put blame on. My university (in eastern EU) had majority of textbooks available for free. We could print them ourselves, have them printed at school, or just buy used. I'm sure it wasn't the case for all curriculums, but probably for many. Writing textbooks is one of the things teachers (professors) do after all.