In November, Bitcoin was announced to be in two futures markets. Big banks and wealthy individuals started buying as much as they could, driving up the price to over $19,000. The first contract expires at 4pm eastern time with a target of 15K. The massive sell off is from the same banks and wealthy that bought in November as they also took the short side of the first future contract, they have still made a profit from these sales.
When that contract expires in 30 minutes, the same people will be buying even more than their original purchases as they have more money from the futures bet.
They are long on the 2nd contract that expires in 10 days. Check my timestamp, it's 3:30 EDST. The price will go up starting in 45 minutes.