You're missing the process by which textbooks are chosen. The professor, or one of his friends, writes a textbook. That is now the required textbook for the c

You're missing the process by which textbooks are chosen. The professor, or one of his friends, writes a textbook. That is now the required textbook for the class, and the professor gets a cut of the profits. Some textbooks are so good or popular that they are used by everyone, even if they aren't the author's friend. (Examples in CS: CLR, Dragon Book.) The students must get the official textbook for the class, because all the homework exercises are assigned from that book. It would be nice to see some effort for open source textbooks, but I don't see them being adopted in K-12 or colleges.