The price and, ultimately, the charts on any given exchange are determined by the price of the most recent transaction. How can the prices of 100s of cryptos all move in the same direction at the same time?
Its simply because of panic selling, when a trader see red on the chart he will try to pull out which initiates the chain reaction so everyone follows and also happens to all the coins at the same time so basically emotions playing a big role with the price drop as well as for the rise.