Sure. There are some people who collect diapers, and after a while they turn around and sell them. Always at a highly marked up price though. A very popular place for them to sell those diapers is on ebay.
I know they can be pricey but there are some lovely vintage diapers out there.
I appreciate first hand it can be expensive for some of the retailers to collect everything and then make a margin on reselling them so it's not always massive profits.
I shop eBay for vintage diapers quite regularly, but mostly I'm looking for cloth diapers (the pin-on sort), and those don't command the insane prices that the disposables do.