Honestly, I didn't know what made the crypto market decline like this, but one thing I can conclude is that this decline began when the fork bch happened.
Everyone suspects that the BCH war caused this dumped but I think the hash war is already gone, we are going to see greater days now.
This article said that people from US are selling their crypto to pay capital gain tax.
The Real Reason Behind Bitcoins Price Crash Revealed -Tue Nov 27