The audience of Amazon product reviews is other customers, not the developer. "Don't buy this product, it's a piece of shit" is constructive, helpful, actionable advice to other customers.

It is desirable if you're trying to build a helpful community where customers help other customers differentiate between good products and products that sometimes don't work on arrival or have software reliability problems; a community that recommends to avoid certain companies is a helpful community to have for a buyer.