btc and other cryptos has been introduced into the futures market and also some exchanges provide the short sell option of them which can damage the price and make them fall very badly.
I am not sure what reasons behind this effect but as everytime i see bitcoins falls everyone is following. But there are other possible factors might involved in this situation, like the competition between cryptos that new one is making some names in the community. just like in bitcoin usually in the month of March usually bitcoin is falling because at this point some bitcoin users hold their bitcoin so that its price is falling but when year month end enters bitcoin start to increased.