maybe there are 2 kinds . . .
kind one: buys a gun, likes it, keeps it.
kind two: buys a gun, doesn't, doesn't.
Not to start a fight but it may be that a lot of people buy guns only after taking a lot of time and effort thinking through their decision, trying and asking to see if they like the gun, then buy it. These people are likely to hold on to the gun. I'm this kind, because I don't have much money to spend and have to work hard to get it.
Others may not consider so carefully, and end up buying a gun they don't like. Maybe they didn't have time to research, maybe they got a bad specimen, maybe they bought before test firing or even holding the gun, either because they were offered a (maybe not so-) good deal or because they had it shipped. But whatever way they were purchased, I'd bet that a lot of those sold with between 10 and 50 rounds through them are these types of guns - the buyer wasn't sure, and got a gun they ended up unhappy with in the first place. They may not have intended to buy it to sell.
Oh, there's a third type. The Dealer. He's in it to buy and sell stuff, and happens to like guns.