Because bot selling. They are mindless. It happen to all alt coins. There is always someone who is willing to sell cheap coins. It happen to black coin, dogecoin, at some point. They need those BTC real bad. They dont care about price. Just sell. Maybe they need BTC to buy some drugs at silk road. That is bot auto sell at certain timing , dont care about price, use the BTC auto buy drugs at silk road , and those drug auto deliver to owner. Everything is auto.