The rising and falling prices are in accordance with supply and demand, as is the case with other traditional tradable assets. In the case of bitcoin, for four consecutive years now, prices are taking a big hit in January and usually pushing in mid-February and beyond. It could be that most traders are currently trying to diversify their assets. There is no definite answer but it is very likely that most traders are cashing in for personal or other expenses and prices are starting to fall because of the case.