Please explain how come many are, maybe you did something wrong.
http://www.ebay.com/itm/10-Amazon-com-E-Gift-Card-Amazon-/111668291355?pt=LH_DefaultDomain_0&hash=item19fff2e71b
http://www.ebay.com/itm/5-Amazon-E-Gift-Card-Email-delivery-No-expiration-Read-Description-/171784222565?pt=LH_DefaultDomain_0&hash=item27ff233765
If ebay finds it they remove it. ANY digital item. Ebay can only monitor so much. Or if reported by a user it expedites the process. Anyway I dont see you getting $10 for a $5 card. Also keep in mind ebay and paypal takes a lot in fees plus you have to worry about chargebacks since both offer no protection for digital items.
same goes for the bitcoin sellers and other altcoin sellers that sell digital items. ahh watch the auction my friend it will go to 10 bucks, seen it many times this week.