I don't think it's competitive, it's suicidal. No rational storefront would ever tell you all the terrible things about the products they stock, no matter how large or small they are. It's insulting to the suppliers and more importantly, stops people from impulse-buying big-ticket products.

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.