Every general store in every town everywhere can't possibly stock millions of individual products. When some item has a potential customer base of a few tens of thousands of people in a country of hundreds of millions, most stores would never get a single sale for that item. But when you can serve the entire country at once via the mail, having a single centralized warehouse specializing in that niche category of items is quite viable.
The only difference with Amazon is that you are buying from a single website, rather than going to the website of a small webshop specializing in your flavour of niche items. And the drawback is that Amazon has zero quality control, so rather than a store where you can browse for known-good curated high-quality niche items you will instead be drowned by piles of absolute garbage - with the occasional decent item hidden in between.
Sure, Amazon might beat your local store, but that doesn't mean it is good for buying niche items.
But in the last couple of months, as I progress through a kitchen remodel and more importantly a kitchen reorganization, I've been seeing precisely this phenomenon every time. The most visible signs are the machine generated "brand names" ("Howonder", "Jaico", etc. etc.), closely followed by multiple instances of clearly the same low quality, SE-Asian-manufactured product being sold under 4 different brand/product names.
I think the difference is that in the past, I've actually known the product I was looking for, and amzn showed me that one and little else. At the moment, I'm casting blindly ("stainless steel kitchen turntable") and there it is: low quality, uncurated crap, everywhere.
Still .. not yet quite as bad as Aliexpress :)
[disclaimer: i was employee #2 at amzn]