Some people don't want to have a game collecting dust on their shelf. Some people like the convenience that GameStop or other trade-in places offer by getting an instant credit on the next game they want to play. Some people don't like or use Gamefly, so they use these trade-ins as temporary "rentals" for some games.

I know everyone wants to cry that developers are getting left out, but the fact is the developers got their cut of the game sale when GameStop or whoever bought the copy, not when the consumer buys it from the store.

Obviously there are ways to make sure more new copies of your game are played, but to simply assume that a person who bought a used copy would have bought that copy at $60 before it got to the bagain bin is just ludicrous.