Many (most?) people that invested during the Dec-Jan explosion did so on the expectation of a profit return, not due to a perceived value in the underlying coin/company.
Many of these people are also inexperienced investors and likely took an out-sized risk. I.E., they bet more than they were willing to lose. Remember, they were banking on everything only going up, not down.
So, when the market begins to tumble, these types panic and sell to cut their losses.
Right now, it is not clear why the panic selling would stop at all.