It's because more and more people are buying bitcoins while hodlers keeps on holding and there where the law of demand and supply enter.
Well said and if the number of bitcoin users who hodl are more than the people trading then the price will automatically spike up... which seems to be the case here and the opening up of bitcoin futures on Chicago Board Options Exchange has also being a major contibutor to the growing price of bitcoin.
This is exactly what is taking place now. The supply of btc circulation is very low compared to total number of traders and there is lack of bitcoin in the system. This will be causing a price inflation next years.