I heard a rumor that it's because Visa/MasterCard don't want to update every point-of-sale terminal in the country.
In 2015, if you implement EMV, and take a chip-and-pin transaction at the point of sale, and the card itself is counterfeit, then you won't be liable. If you don't support EMV, the liability will be the same as it is today. If you do support EMV, and the fraud is something other than a counterfeit card, the liability will be the same as it is today.
It's almost as if they designed the incentive to create a talking point when selling the EMV hardware to retailers, without actually shifting any meaningful liability away from them, so the card brands and banks can continue suffering none of the losses due to fraud outside their merchants' reasonable ability to stop.