That may be so. But there also may be an opportunity for Amazon to target ads better than anyone else could. Essentially retargeting for Amazon's platform.
Maybe even more importantly, they know which products you returned and why. Public reviews on items are one thing and likely gameable, the direct merchant feedback form remains private between the merchant and the customer. And Amazon, of course, because they mediate the exchange.
For pure marketing purposes that kind of limited view could be quite valuable indeed.
As to what this means for me? More rules in AdBlock, I guess.