Although I am against goverment control of most things, including college textbooks, the answer to this question should be obvious: College faculty often require their students to purchase the latest edition of the textbook that they or their collegues have written even though the changes to the latest edition from the previous edition are insignificant. The result is that a student spends $150 for a new book, rather than $30 for a used prior edition of the same book from the same author, and the only difference between the two editions is a footnote on page 442, the size of the graph on page 561, and correction to a citation in the bibliography.
Do they get kickbacks from the astronomical prices of the newest books?
One scheme that might cut the cost of textbooks would be to release all in a binder format, where future updates would consist of small kits to replace superseded pages and every effort would be taken not to upset pagination.