The problem is eBay is pretty much the only market, so like the phone company, we're stuck with them. Amazon could probably create some true competition, but Amazon doesn't allow the sale of used clothing. And Amazon charges more than eBay does, anyway.
Of course, the possible exception to my statement above is Etsy. I've seen a couple shops on Etsy that do pretty well, but they'd still have a long way to go to deliver the volume of buyers that eBay does.