I wonder why Sony or Microsoft don't try to 'game' the used market by becoming the used marketplace for virtual copies. They can charge a commission for every game that changes hands.
I'm sure they can think of some things to make new copies a differentiator such as DLC's and perks in game.
Also, 'new games' eventually get discounted as the title gets old. It's one way of keeping money in the game store ecosystem constantly changing hands.
A used game market provides downwards pressure on new games.