I guess I don't fully believe the story about the single review causing such disproportionate harm.

I do, who's going to take a chance of receiving a biohazard lol

This just feels like a case of folks having too many of their eggs in a single precarious basket.

this is true, but Amazon's position in this space means their the default choice in many cases. It also rings true that due to their gigantic market presence, they don't have to worry about being outcompeted because of their own mistakes.