These are the following ways in which Amazon is not like a (WalMart, Costco, insert retailer of choice):
* Physical retailers do not have access to the same breadth and depth of data that Amazon does. For example, retailers have no reasonable nor accurate methods of determining which advertising methods bring in the most leads. They have no idea how many people look at the product without buying it. They have no idea who puts in their cart and then lets it sit there for days on end. They have no idea who puts an item into their wishlist. They have no idea which people look at it, then come back a week later and buy it. They have no idea how many competing items, let alone which ones, the buyer compared it with before buying. They can't calculate conversion rates, nor satisfaction rates. Maybe if they're lucky, they can track returns down to the purchaser (because they might require a receipt to return), but they likely don't know much about who you are or why you're returning it.
* Retailers can't notice you looked at a product without buying it, then follow you around to your bank, your barber, your job, your home, relentlessly trying to convince you to buy it.
* Retailers can't look at your general preferences across thousands of unrelated products, perform machine learning methods to determine your likelihood of conversion for different brands and products, and then rearrange their shelves specifically for you to optimize visibility of their products for maximum profitability.
* Perhaps most importantly, retailers always have an incentive to sell their inventory. They buy it, they invest labor into presenting it, they pay holding costs to keep it in stock, they relentlessly optimize within difficult physical constraints to provide visibility to its location on the shelves, and they advertise its existence to the public. Amazon has none of these costs or incentives. If they decide to tank the listing of a competing item, they bear no cost in doing so. They are being paid for every single cost incurred, and they're making money off your stuff in FBA even when it doesn't sell. Even pure consignment stores will regularly decline to consign products that they don't think they can sell or don't think they can make enough money on to cover their costs. Amazon has no such incentive.
Does Procter and Gamble hate the fact that Costco can position Kirkland Signature right next to their products? Of course they do...but they still sell their product. The same can't be said for many private sellers of niche products when Amazon launches an Amazon Basics competitor. Their listings get tanked, their recommendations disappear, their sales effectively drop to zero almost overnight, and if they made the bad decision to use FBA, they're stuck paying holding costs and eventually shipback or disposal costs in order to exit the market.
Amazon is uniquely positioned to take advantage of marketplace data in ways that retailers could never feasibly do, and they bear no costs (and may even augment their profits) when they put their merchants out of business. They absolutely need to have their marketplace either shut down or completely separated from their retail space by legally regulated means.