I think they also provide the economic information needed for control. Much like FB can give them all of people's social information (ideologies, religious affiliations, associates, etc.), Amazon can give them our spending habits. This information can be used to better craft their control.
As outlined in "Silent Weapons for Quiet Wars", their ultimate goal was an controlling computer system (AI) that had complex algos driven by all of the data they mine (FB, Twitter, Amazon, etc.) for more control. Amazon could be the source of the economic inputs.
Bill Cooper - Behold a Pale Horse (Ch.1)
https:// wikispooks.com/w/images/b/bc/Behold_a_Pale_Horse.pdf