Or, in some cases, people bought them to try them, disliked it, decided against it, or simply changed their mind and sold them. It happens hundreds of times with all likes and manners of various knives. In this instance it is much more noticeable because it is currently relative and on people's minds.
I would bet that if you asked any of the secondhand market buyers of said knives if they felt forced or somehow coerced into purchasing the knives, regardless of price, they would respond with a resolute "no, I purchased it using my own free will." I would also bet that they would be grateful to have had a chance to buy one--even if they had to pay a small premium.