There is a famous VC slide from 2010 showing Craigslist being "unbundled" into Airbnb, Tinder, Zillow, and Indeed.
The same thing is happening to eBay.
Depth > Width
Generalist marketplaces are wide and shallow. They sell everything, but they know nothing about what they sell. To eBay, a PSA 10 Charizard and a used toaster are both just "listings."
Vertical marketplaces are narrow and deep. They know:
The Feature Gap
Because eBay has to support everything, they can't build specific features for anyone. They can't build a "Set Registry" for coin collectors because it wouldn't make sense for shoe buyers.
Vertical marketplaces can build tailored features that lock in their users:
This is why we win. We are building the features that eBay can't afforded to build.