eBay I think had their growth capped once you had Etsy, Amazon FBA, and other options on the field.
Your average normie has no interest in the hassle of selling their used stuff (which has, if anything, got harder in my 25ish years using eBay), nor of buying random used staff from anonymous individual sellers.
Etsy covers the arts & crafts coded goods (though much is now China dropship).
Amazon allows the big merchants to sell to normies who just want to click "buy" without thinking about seller rating risk, when something will arrive, etc. Basically most people have no idea they are buying from not-Amazon, because it says amazon.com and that's good enough. eBay never had the smarts to create that user experience.
Because you're a used <pick niche> dealer or a dealer of something that is on the large end of what you can send in "normal" mail. Tires come to mind, even on Amazon very few of them are actually FBA.
Your average normie has no interest in the hassle of selling their used stuff (which has, if anything, got harder in my 25ish years using eBay), nor of buying random used staff from anonymous individual sellers.
Etsy covers the arts & crafts coded goods (though much is now China dropship).
Amazon allows the big merchants to sell to normies who just want to click "buy" without thinking about seller rating risk, when something will arrive, etc. Basically most people have no idea they are buying from not-Amazon, because it says amazon.com and that's good enough. eBay never had the smarts to create that user experience.