Unlikely? I literally just described an example of Costco doing this right now with vodka. That's not a hypothetical - Kirkland brand vodka is a real thing.
Your logic is backwards - when space is at a premium, making the most profit off each item in that space is critical. It makes more sense for Costco to do this than it does for Amazon, not less.
Store brand products are not new and not the issue. Let's pretend that Costco didn't currently sell vodka at all. If Costco wants to know if they should start selling vodka or bottling their own vodka and selling that they don't have access to the sales data from the liquor store next door to Costco. Amazon is letting other businesses take the risks and using sales data from those businesses to outcompete them.
That's the right way to look at it, missing just one crucial detail.
Costco pays for the items that appear on its shelves (excepting the <1% of goods that are on a consignment basis, usually new trial products). The distributor of the store brand and the name brand have already been paid for the products (and are usually the same company).
Amazon gets paid by the distributors (aka third party sellers) on Amazon.com for handling their sales (even in instances where it is not handling fulfillment), while also competing against them. That is where the anticompetitive concerns arise.
If Amazon just sold stuff through the Amazon.com seller, and didn't have third-party sellers, (or if it operated a separate website for third party sellers) that would be fine.
Don't most large brick and mortar retailers maintain refund for unsold goods agreements in addition to defects? Generally only exercised if they are complete failures.
Effectively the difference in practice is a matter of financing and grain of operation - older retail would gain more and give no extra to upfront sales of say toliet paper after a demand spike raised prices while Amazon would give them a per sale percentage cut.
At what point does own involvement in consignment sales models become not fine? If it works at 1% consignment. Is it 25%? 50%? 75%? 90%? Or more likely it doesn't exist because the whole concept is a fabrication that pays no attention to real law and operates in the court of public opinion to push their bullshit which wouldn't even need a defendant motion before winding up dismissed by a judge because they cannot point to any real laws?
I don't know why HN is so focused on consignment sales. They are a tiny portion of the retail market, because no store (even Walmart) has the leverage to force consignment terms on their suppliers except for the tiny portion consisting of new products that distributors are trying to get stores to start selling.
Also, Amazon does not give a per sale cut of the percentage, nor would they, since that's not how consignment works. Consignment goods are still sold at retail price; the only difference is that the supplier only gets paid for goods that sold. They don't get to share in the (additional) profits if the retailer (aka "Amazon.com")charges more due to spiking prices.
But Costco does sell Vodka and wouldn't have made that product if Vodka sold 10% of what it actually sells. Because Amazon sells literally everything, is it a crime to do what Costco does, just on a bigger scale?
The only end-goal that would actually solve the problem fairly is if companies couldn't sell first-party products (or products from a partner where they have a vested interest in) in their store. If you just take care of the one company, you end up with other companies doing the same thing in 20 years like how iOS still has a default music player when MS got burnt for that with having a default browser.
I feel like people in this thread are being deliberately obtuse. The issue isn't about selling vodka. It isn't about selling store brand alternatives to brand name products. The issue is where Amazon is getting their data from when decided what products to sell and what store brand products to make.
When Costco decides to make a store brand alternative they are using sales data for things they have sold in their store. Amazon is using data for things other people have sold. Amazon is not doing what Costco does.
This is not about making a home brand. Amazon can literally look at the sells data of e.g. some seller which sells Nike Air Jordans (as a stupid example) and go and source those themselves and offer them (the exact same brand) cheaper than the seller, because they have all the sales data. Now how would Cosco do this?
Your logic is backwards - when space is at a premium, making the most profit off each item in that space is critical. It makes more sense for Costco to do this than it does for Amazon, not less.