Probably because it happened last year, and the year before it as well. And in that regard people will just assume it will happen again, which you seem to think as well. As result you will see people anticipating on a likely break-out in the price by starting with buying up some "last minute" coins, in order to be ready to sell when the price really rockets up.

Right now all pieces seem to fall in the right places. Sentiment is good, people seem to believe that the price will increase further, Segwit that might get activated this year, overall demand has increased a bit, etc. All these things combined make the market behave like it is doing right now.