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.

Amazon fulfillment, That’s the killer. Why bother with another marketplace when vertically integrated Amazon does it all

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.

> online auction business

Do they even do it nowadays? I was under impression it turned into an ordinary marketplace, probably with a bit more focus towards small/private sellers.

Yeah of course they do. And it’s still used by people looking to get deals.

From my perspective, eBay has a solid niche of older items, and they tried to break into the buy new items market too, but the hassles of selling mean for the most part only scalpers sell new items on eBay. Although there's some niches where it's not unusual: new auto parts seem common, I guess it's easier for a dealer parts counter to run an eBay store than otherwise.

I find that for a lot of "cheap junk from China" gets cheaper when you eBay it directly from China and cut out the cost of the Amazon middle man.

Recently I bought a chainsaw tool on eBay from China as I didn't want to buy a 6-pack for $10. I was able to buy a couple for about $0.20 more per unit. Sure, higher unit price and they'll be here slower but it's several $6ish saved.

ebay seems relatively competitive with aliexpress, sometimes even cheaper. amazon everything seems to cost much more

Amazon has free returns on almost everything, so if comparing prices for the same item, the cost of free returns has to be added.

I mostly use eBay for buying computer and bike parts - e.g. my most recent purchase on my work (tax-exempt) account was a batch of a specific model of 40Gbit NIC, and a specific type of bike seat post on my personal account.

The eBay search function isn't great, but it's vastly better than Amazon, where search results are polluted by large numbers of garbage sponsored results - this may be related to its success in these niches. (although in my case it's partly because I can avoid paying for Amazon Prime, and still choose things based on prices that include shipping)