They don't do anything about it because it's a feature not a bug. They know full well about all the fake reviews, fake products, product switches, counterfeit products, dangerous products, etc., and choose not to do anything about any of it because it's making them money. Amazon is basically an online real estate company that owns a giant online mall full of scammers, snake-oil salesmen and fraudsters, but they get to keep cashing the "Rent" cheques from these vendors in their "Mall," and so they don't give a single solitary f*ck about whether or not actual end customers suffer as it's not them doing it, just the people who rent space in their mall.