If you want a box of rawlpugs, some rope, a bit of plastic sheet and so on eBay is still better than Amazon.
Got 25m of edge strip off eBay with two day delivery. Amazon didn’t even list the product I wanted.
Ebay better than amazon for them because the sellers list the items on ebay rather than amazon.
Both sites require sellers to list items for sale. Amazon is of course also a retailer in its own right so a competitor for mainstream items available from suppliers.
And like all retailers they don't bother spending the money on stuff that doesn't sell quick enough. The small sellers will.
A seller may list an item that sells one or two a year and secure in the knowledge amazon aren't going to start stocking the item.
A seller may list a top 1,000 toy in the run up to christmas and have several dozen competitors on the same page including amazon.
An item that sells every 5 minutes, risk is the sheer number of other sellers and the elbowing off to the side by amazon.
This year, like most years, I purchased most of my christmas presents from the two sites. Plus Etsy for items not available on either of those two bigger sites. Speed wasn't essential though of course needed delivery in time for christmas. Item itself was the main driver in where I would purchase, not price or speed of delivery.
Sure, Prime delivery is nice - getting the item on a Monday rather than a Tuesday is not always a good thing.
So waiting an extra day to order because they are so efficient! I'm better getting delivery on a day I'm at home and not stuck in a meeting.