I'm not sure why anyone would see any reason behind Amazon's move to hoard a bunch of gTLDs (global top level domains), other than pure greed.
In a recent open letter (PDF) to ICANN, Association of American Publishers rightfully opposed granting Amazon the control of the .book gTLD. It states:
In short, Amazon makes clear that it seeks exclusive control of the “.book” string solely for its own business purposes, notwithstanding the broad range of other companies, organizations and individuals that have diverse interests in the use of this gTLD or its second-level domains by others or themselves.
Well stated, but does ICANN or anyone else really need a protest letter to recognize Amazon's true motives in hogging as many domains as it can?