Now that they've captured 50%+ of US ecommerce, they've also raised many prices, to the point where they're far from the cheapest price in many cases. A random example... the cat litter I just purchased is $17.89 at Amazon, $13.49 at Walmart. Last week I bought a chair mat for $21.95 on Ebay - identical item on Amazon was $33.95 (both including free shipping but Amazon came with an additional 8.25% sales tax).
They can do that because so many people don't price compare anymore before going to Amazon.
Not to mention the issues of buying an expensive brand item and getting a fake instead, as well as the large numbers of fake reviews. Indeed, it is pretty hard to get started in Amazon FBA these days when your competitors all have hundreds of glowing reviews for similar products and you have none.
They've also moved many items to the add-on category (no more free shipping unless you have $25+ in the cart, even with Prime).
My Prime membership expires in a couple months time, and this time I'm not renewing it, after being a member for several years.