Do you expect Gamestop to buy a game back for 100% and sell it the same amount?
Do you expect them to buy a used game from a person for say 30 dollars and them not sell it for 35? Its called profit.
If they actually bought them for £30, I'd laugh. But they don't. You're lucky if they give you a fifth of that unless you intend to trade the game in for another (at which time they just make even more money off of you). You make it sound like they don't make profit from the sales of game consoles, accessories and new game sales - which is nonsense, since over here they make a little less than £50 of profit from every 3DS they sell. That's likely more than they've ever made in terms of profit per console sold, but it's no secret that every console maker gives retailers at least 10% of the console's price as profit.
QUOTETheir job isn't to donate money to game companies, its to make money.