It's not an anti-trust case because there are literally thousands of other retailers - both online and brick&mortar. Amazon has nowhere near a monopoly on anything here, they are running a store. Just like walmart, target, costco, Safeway, etc - all of which have their own house brands.
I find it incredibly hard to believe that Amazon is not a monopoly. This Forbes[0] article from 2013 states that Amazon had more sales than it's next 12 competitors combined, and that it's sales were growing faster than overall online sales. If we take this as read, that means Amazon is probably more dominant in 2016 than it was in 2013.
That doesn't seem like meaningful competition, that seems like the other retailers are keeling over.