Trade-ins are for chumps. You're stupid if you trade in a car. Plaiun and simple. The dealer rapes you on it, then turns around and make another 70% minimum off you.
Sell it yourself in the Autotrader. It's not hard at all.
I think it comes down to patience. People just decide they want a new car and can't be patient enough to take the time, sell the car themselves and then go buy a new one.