Food is a consumable necessity and car prices can be haggled; cars also aren't originally sold in cellophane.
I don't know what else it is but I just don't want to pay full price for a game with stickers on the case and artwork that I can potentially damage while trying to remove that may also have a grimy scratched case and game.
Especially since those are the qualities that accommodate many used games hence their lower price(yes I know it's possible to find mint used games too).