If Amazon were competing to win customers, they might do something like this to increase trust in the quality of the products on their store. Of course, that's not Amazon. The only significant threats to Amazon today are anti-trust regulators.
You might argue that showing these "boycotts" would stop people from returning these products, but it would also curtail a whole lot of buyers that would consider it "good enough". Amazon deserves their fair shake by the FTC but if you think this is the reason then you've got pretty bizarre expectations.