Kotaku Australia, "We’ve just learned that a directive, sent to all EB Games stores, has asked that all copies of Elder Scrolls Online — including the pre-paid cards — are to be sent back to the publisher."
The Elder Scrolls Online launches Seasons of the Worm Cult today on PC and Mac, and Wccftech has all the details straight from the developers.
MMORPG The Elder Scrolls Online is celebrating its tenth birthday by rolling out a large number of improvements and changes.
ZeniMax Online Studios announced that the MMORPG Elder Scrolls Online will soon receive a new feature called Subclassing.
I can't think of another valid reason why they would remove the prepaid cards from the store other than making the game F2P.
Edit: posted before the update
Unless you are blind, this is an obvious sign of FTP implementation. TERA went through the same deal, right before the game went FTP. All of the retail copies vanished as any account with a retail key were awarded founders status when the FTP servers went live.