This is from the FAQ here:
eBay has changed the terms of their affiliate program, and is not currently approving applications of people that do not operate a site on their own domain. If you have an approved ePN account you can use it on HubPages. If you do not have an ePN account, you are very unlikely to be approved by applying using your presence on HubPages. If you have a site on a domain that you own, we'd suggest applying using that site.
It helps to read the help files when you join a site.