Why isn't there yet a good marketplace like Amazon/Ebay using exclusively Bitcoin for people to sell new and used merchandise worldwide?

I've been searching for marketplaces like this for a while now, and I can't find any serious business having done it yet and it just seems obvious to me that it would be a good service to develop. What are the impediments to have a real worldwide marketplace like this? via /r/Bitcoin http://bit.ly/35xDFQB