Could be a number of reasons. I've done a few trades only for different reasons. the easy of the deal mentioned above is usually the primary one - we each get a game we want and it's over and done with. In other cases, I don't "need" the money, I like having games, and in a lot of cases my games are worth more to me personally than people would want to pay me in cash, but in a trade situation people seem easier to deal with when it comes to give or taking a few bucks either way.