So for me, Amazon still offers a wide range of items and selection, many of which I would be hard pressed to find in a nearby B&M, and usually for cheaper (at least there are more price points to choose from). A recent example is some gold chainette fringe. I was actually in the fabric store and they had some but not enough, and I found a suitable replacement on Amazon for about 1/3 the price.
I'm not saying it's great that Amazon is allowing this stuff, my point was just that, even with the presence of some noise, it's still a quite useful service and it seems silly to act like it's "over."
What you apparently don't understand is that Amazon co-mingles inventory from everyone who ships them a particular product.
It doesn't matter if you buy an "Apple USB Power Adapter" from Amazon, Apple, or Shady McCounterfeiters. You get a random sample from the same pool of goods. And that pool of goods often contains counterfeit products (in this particular case, about 90% are counterfeit).
Basically, Best Buy doesn't just sell anything JoeBlow45 who created their account yesterday decides to dump on their site, they have real suppliers and they know what they are selling.
And the listings don't end up like this: https://www.amazon.com/Paper-Illusions-Hearthstone-Colored-W... it's a listing for wallpaper but the pictures are for a Grateful Dead plush and another picture is a Grateful Dead poster.
You might be surprised. Many big box sellers now include third party listings from anyone and everyone. I believe Best Buy discontinued this last year or so. But many still do. Newegg, Walmart, Sears, to name a few.
If I want nicer headphones I can go to a brick and mortar retailer (or their online counterpart) and get a selection of curtailed products from known brands provided by known suppliers with all the information about the products listed with a good search so I can compare. I have a choice but I don't have to slog through dozens of private label brands or poorly listed products with missing or incorrect descriptions/information. Or irrelevant products listed in the wrong product category.
If I go to Amazon I have to wade through pages of bad search results full of junky unsafe products from questionable sources (paradox of choice) with bad/missing information just to roll the dice that I don't get something counterfeit and/or unsafe.
What purpose does Amazon service now in this situation?