Because Banks in Britain and the United States have banned the purchase of cryptocurrency by credit card. This is bad news makes bitcoin and cryptocurrency market are going down. 
It seems bitcoins are not performing well these days. But this is not the fault of bitcoins, rather all those people who become panic and sell bitcoins. This create a number of bitcoins available in market, thus demand gets low and supply becomes high. Results shows us the price of bitcoins so down now. People need to understand about the nature of bitcoins. Still good luck everyone.