The main triggers of human behaviour are basic emotions, such as joy, anger, fear etc. I think that fear is stronger than joy, because if humans lacked it throughout the history, they wouldn't have survived. When people see bad news they see a threat to their prosperity, just like a wild animal used to be a threat to one's life. They react simultaneously by decreasing the risks to the minimum and thus causing the panic selling. J. Rawls wrote that rationality of people makes them choose to lessen the risks rather than increase potential profit. As now is the time for the latter, people are still behaving carefully, for they want to make sure they will not lose money if they buy cryptos now.