For me there might be some series of events which is eventually taking bitcoin down. Such as the hacking and and the regulations, this is very known to us that scammer is just only waiting for a timing. In this way there are lots of investors got scared and left bitcoin. Another reason also is that some of the people still don't know how to analyze on how to maintain to earn a money,some investor was just put their money to get  higher return faster  So when statements related to Bitcoin Bubble came out and all these events began to happen, people thought that the bubble might be real. This made them pulling out their money from the market. It is called following the trend and is a most important factor that sometimes lead to disastrous falls like this one.

But don’t worry, in the eight year old history, Bitcoin has always bounced back.