Amazon doesn't eat its own dog food. So what? They don't have to: the company is so big they just don't have to show anybody that they believe in the quality of their own stuff enough to use it themselves.
Just like Microsoft used to sell Windows server but ran BSD internally, because they're not stupid: that didn't prevent them from inflicting and imposing Windows server to countless companies around the world and making a fortune out of the wretched thing, because Microsoft was kind of unavoidable.