I doubt they would run across that many defective games.
I'd wager their like new cases/manuals were from rental stores. They probably had an agreement to buy cases and manuals, since rental places had no need for cases/manuals. That might also explain why their selection is so pitiful now since very few rental stores exist these days.
Their used stuff was probably from trade ins that either had the manual or case, so they just sold the item as game only and sold the manual/cases separately.
You could always contact them. They would probably consider a bulk purchase.