Amazon does not need to make a profit off of books, for a variety of reasons. It can therefore sell them at a much narrower margin, or no margin, or even a loss

Amazon does not need to make a profit off of books, for a variety of reasons. It can therefore sell them at a much narrower margin, or no margin, or even a loss. Other booksellers generally don't have the many additional sources of funds that Amazon does. So if they compete with Amazon on price, they lose money and go out of business. And if they don't compete with Amazon on price, customers go to Amazon and the bookseller still goes out of business. Bit of a rock and a hard place for the booksellers.