People sell for various reasons. Currently my belief is there are three types of people selling. The biggest being the MtGox Bitcoin holders which want to liquidate no matter what. Next you have people who have too much of their money in crypto and due to upcoming bills need to get out soon. These people panic sell sometimes for valid reasons for instance maybe at sub $9k bitcoin prices they couldn’t pay taxes on last years profit. Finally you have the weak hands who see the first two people selling and lose their faith.
a forth type of people selling at dips: Those forseeing the dip to go further, and making their plan of selling now and buying latter at a more cheap price, a way of collecting some profit this way.
True, traders will always exist :)