That is what is called predatory pricing. Since bestselling e-books and A-list books, which is what Amazon was selling below wholesale cost, not to mention retail price, accounted for 80% of the revenues of e-Books, there literally were no profits to be made in e-books so no competitor could even think about entering the e-book market. Even the publishers of e-books could not profitably sell e-books against the Amazon Leviathan at the pricing structure they were forcing on the e-book market. The sales of the balance of e-books, the non-best-sellers and non-A-List e-books, could not ever make up for best-sellers and A-list e-books being sold for $5 to $8 below cost. . . especially when Amazon was selling those books close to cost as well. Amazon's 90% stranglehold on the e-book market had to be broken and the retail prices of e-Book raised to rational levels to actually support the industry for the market to be healthy and support the authors and support the market. Amazon's artificial $9.99 price did not leave anything to do that.
Amazon turned the economics of books sales upside down. The Best-sellers and A-list books SUPPORTED the sales of every other book in inventory. Those were the bread-and-butter sales that paid the bills that allowed book sellers to even HAVE the rest in inventory. You cannot keep the doors open the other way around. Amazon had almost killed all of the brick-and-mortar dead-tree book stores by doing the same thing in paper and hardback books, selling the best sellers and A-list below cost. . . a price no one else could match or compete with and keep their doors open. Amazon could do it because they weren't supporting brick-and-mortar stores and subsidized the cut-rate sales with sales of other products and NOT EVEN TRYING TO MAKE A PROFIT!
For it to be predatory pricing in the US, Amazon would have to be selling the e-books at below sellers cost. If they are making any profit regardless of how small, it isn’t predatory pricing.