Ask HN: Why haven't online auction/general-marketplace sites been disrupted yet?

This question (title) is born out of frustration in trying to teach my mother how to use eBay on her iPad to do simple occasional buying/selling.

Needless to say, it hasn't gone smoothly. I can't believe the complete and utter disconjunction between the various areas of the site, let alone between the apps and website. It's barely usable.

And whilst I understand a lot of the headaches and hoops they force you to jump through are to cover their own backs in attempts to protect both buyers and sellers, it's still just a complete mine-field.

Is there any good reason that sites like eBay, Craigslist, Gumtree, etc haven't been pushed aside by a sleek, modern, UX-focused SV-startup yet?

I could easily see eBay being what MySpace was to the social-network space in 2007.