According to CNBC, federal prosecutors had launched a criminal probe into the cryptocurrencies earlier this year based on suspicions that their price was being manipulated. I think it might be the main reason behind the price of bitcoin dropping to around $4000, but I also wonder whether it could be that authorities are afraid that Bitcoin and other cryptocurrencies are taking over the financial system since they're now so popular.
I guess some people are just disappointed with the price now expecting for it to go up just like last year during this time but then the opposite happened and it keeps going down. With this kind of market, some I believe already gave up and sell their coins with no plans of turning back again. Some panic sell seeing the price continuously go down. With the news about the fork of bitcoin cash, others sell their bitcoin for bitcoin cash to have the free coins and then the price wasn't able to recover.