If I'm looking to buy a game totally new, and when I bought it I can play it as if it's totally new, then I don't care if it was used before. I got exactly what I wanted and paid for in terms of gaming experience and price.
Now, if I wanted to buy new and got a copy with scratches, or smudges, or with cartridges save files on it. Or with codes, where the code was already used. Yes, that's a different matter. But no store in their right mind would sell those as new.
Furthermore, what's the big deal? 'Still sealed' is NOT the same as 'new' you know. So the disk was taken out. It has never touched a DVD drive or whatever before, it has no scratches or smudges if the employees did things correctly, and it has the codes that go with it not even looked at yet. So it's still new, just not sealed.