1 - They get old fast. Information is continually changing. New editions make old editions obsolete. Sell the books you've already used to buy something you really need, like pizza. 3 - Recycling saves for everybody.
Books are a reuseable resource.
You not only help save the environment, you help other students save money. 4 - Make a great recovery. Salvage some of yout textbook costs by selling them back to the bookstore. Your books will probably never be worth more than they are right now.