The real answer is, very few authors say “oh I have a great idea for a book that I’m only going to sell through Audible!” They have an idea for a book that they want to sell, and then through licensing deals and marketing it becomes an Audible exclusive.

So the choice is created when the author decides to write a book. The choice is restricted when the author or publisher decides to offer it only on Audible. Writing a book is “creating more choice”, offering that book exclusively through one reseller is limiting that choice.

You might make the argument that this is just capitalism and the free market doing its job, but to keep healthy competition alive capitalism is generally regulated to keep the biggest players from dominating the entire market. Amazon and B&N might have the money to fight over exclusive rights to a book, but smaller bookstores don’t. This creates a barrier to entry for any new or smaller stores who want to compete in the book market. The reason regulators watch for this kind of stuff is because Amazon has the money and the audience to completely lock out any competitors they want, singe-handedly destroying the free market.

Amazon doesn’t need an exclusive deal in order to sell books. They need exclusive deals in order to put their competitors out of business.