Amazon cares about market share and there is a large contingent of the market that cares about ethics. ESPECIALLY when tied to the food they consume. -You seem to be among this cohort. Ethics are something that should be adhered to for the sake of themselves, and not because they wield marketing power, but lets be honest people are putting "GMO FREE" on bottled water cause it's marketable not because it's ethical. *I have no idea if people are putting GMO free on bottled water, but let's be honest... it sounded plausible... didn't it?
Companies like Amazon and Wal-Mart are so massive and so ubiquitous that the loss of income from bleeding heart liberals is of no concern to them unless it affects their public image. If they can bottle Flint Michigan tap water and fool you into thinking it's all natural, GMO free, and get away with it, they will.
Well, part of it is that we as a country allow companies to do this. There are currently no regulations regarding the term "natural" or "all-natural" for food labels. That said, the FDA is currently requesting comments on this exact topic.