I guess you're unfamiliar with Bezos and unfamiliar with how and why Amazon began. Books are not what makes Amazon special. The idea of books came after Bezos designed the system that makes Amazon special.
Bezos studied engineering and computer science at Princeton, graduating magna cum laude.
He then went to work doing IT for Wall Street . From beginning to end, he's been about expanding computer technology. He didn't build infrastructure in order to sell books, he used books and other easily shippable products to monetize a computer based distribution system. You may notice they sell a heck of a lot more than books - because books are an readily replaceable accessory to their actual business. That's why they don't write books, they buy them because books are not what makes Amazon special.
The idea for Amazon came to him while he was traveling a across the country and he heard that the supreme court ruled internet sellers don't have to collect sales tax. He decided to combine that with his skill at building large scale infrastructure and put together a mass market system selling stuff on the internet at a discount. What to sell using the system he designed? It should be valuable enough to ship. You don't sell concrete or soda online, shipping would be a problem. Electronics have high value per pound, but quickly lose value in the warehouse. The post office has a special extra low shipping rate for books, so books were good product to start with. The product was chosen to fit the distribution infrastructure. The infrastructure wasn't built to put his (nonexistent) bookstore online.