Before AWS or their open marketplace model, Amazon provided e-commerce services for established brick-and-mortar retailers (basically, Amazon-run online shops under the established retailers’ names.)

They quite aggressively mined this for data that was used competitively for Amazon's own online retail operations. I'm not surprised that this combined with Amazon making a big move into brick and mortar retail would worry existing retailer, especially Target, who along with Borders was, IIRC, one of the noteworthy retailers that had been dependent on Amazon's earlier service.