This is my theory about why the price is dropping. One of the factors why BTC and other crypto is dropping is because of the supply and demand. As the supply last year is too little and the demand was that high price is very high until the end of October I guess. And then at the end of November when it rapidly increasing and reach the highest peak of price which is approximately $20k many people exchange the coin and keep the profit that they invest and more and more of companies got into mining that added the BTC supply. Because of this event that happen last December 2017 specifically the supply got high and increased encountering the demand of people that's why the price drops.