I think the rapid dropping of price is due to some people that until now still selling their bitcoin in low price because they want to cut their losses due to continous fluctuation of the almost all cryptocurrency in the world market.
I think that one of the reasons why virtual currencies have disappeared from the market to give way to Bitcoin's dominance may stem from the government's desire to manage this kind of assets by law. After the ban on transactions, many countries are changing the policy to control more closely. With the legal support and attention from investors, the collapse of Bitcoin is unlikely or only temporary.