If they would just put the search back to how it was (deterministic) so it would do exactly what you ask for, not one of these modern searches where it kinda bubbles up a few items, but the rest is all random sorta-maybe like what you asked.
They market pretty heavily in growth markets. They're really heavy in advertising in the UK and Europe. There's a lot of digital remarketing they do in the US.
It's about the brand. Ehen shopping online, everyone may have heard of eBay, but how many people are going to go there first, as opposed to Amazon, Etsy, AliExpress, Temu, wherever else. And yes, eBay is going to have the weird eBay stuff, but if users don't even think to go looking there, they've lost a sale.
As one data point, if I want something new, I go Amazon first and eBay second. If I want something used, I go to eBay first. My search usually ends there, but if I can't find it there, I probably have to go to a specialty forum.
Even for bootleg stuff (mostly long out of print arcade hardware), eBay is pretty much on par with AliExpress.
Legitimately millions of people. It also depends on the item but Amazon has been worse than eBay in my experience since at least the pandemic. AliExpress and Temu have some overlap to eBay but also offer a different consistency of experience.