The cost of entering the Amazon marketplace is trivial. The cost of being the first thing a person sees when they search for X is enormous. And since Amazon has its own internal brands, you're often competing against a staple product in a bidding war where the auction house is both a bidder and seller.

This environment encourages tatty plastic shit, because anyone that isn't making enormous margins on their sale isn't able to operate profitably. Its a weird sort of survivors bias in which only Amazon, a handful of well-recognized name brands, and a bunch of shameless scammers can operate profitably.