Are the sellers not able to limit based on CC number? Perhaps not. I know most websites don't actually have any visibility into the payment info that is usually handled by a third party payment processor integration.
Seriously tho, something must be possible. A payment processor feature that has allotment restrictions based on client+card or delivery address must be possible. Payment processors should be jumping at the opportunity to charge extra for that type of protection for clients that are selling limited high-demand products.
Obv using more cards is a workaround, but it doesn't sound like the hoarder even had to go that far.