Well, of course. Why were they going for such high prices when they now seem to be selling at more reasonable ones?
/shrugs. It's just what some people on the internet do. If someone wants something, they'll bring the price up. Ebay is just like that, I guess. Honestly, anyone selling the Pokemon Oreos for over a thousand dollars is ridiculous, anyway, and no one should charge that much for consumable cookies.
Collectors are willing to bid anything to get what they want, and Pokemon is no exception. I'd honestly just go see if you can find Pokemon Oreos at your local supermarket over buying them on Ebay.