This is because Bitcoin Cash is dependent on the success of Bitcoin for its survival as is the case for every altcoin. All the Bitcoin Cash people who have been hating on Bitcoin are partially responsible for what is happening to Bitcoin, and are now reaping the negative effects of the FUD they have been spreading against Bitcoin.

We are in a bearish market, which could go on for a long time. The more Bitcoin goes down, the more Bitcoin Cash will go down and every other altcoin with it. In my opinion, when prices continue to drop with no clear indication of recovery, it's a smart move for a trader to cash out before losing his or her profits. There is a reason why traders say one should sell high and buy low: there is no guarantee prices will go back to what they were.  

This is not financial advice, but my personal opinion.