I do not know the real reason why bitcoin prices drop this big. but I see a graph every year that every year the bitcoin price always comes back at the time of bitcoin prices in November of the previous year. perhaps this decrease is the cycle of bitcoin price movement. However, I think that the correction of the bitcoin price is now a virtue for the future of a digital asset such as bitcoin.
Most of the answer is dont know what really happen.
I also dont know what happen but as i know, bitcoin and other crypto is volatile so the run up and down is normal.
This huge correction maybe because panic sell. The first correction make people sell their asset and continue till panic sell.