Because the students judge the utility of having a textbook available as worth the price (or in some cases the text books come with a code that you have to have

Because the students judge the utility of having a textbook available as worth the price (or in some cases the text books come with a code that you have to have to pass the class). Same reason a book collector may prefer buying a book over checking it out at the library. It is like asking if cooking for for yourself is so cheap and healthy, why do people eat out so much.