I think you are not the only one wondering what happened and what can be the cause of this strange movement. Well, in my own analysis it can be because there remains a shortage of "investors" or buyers in the market and the rise of Bitcoin happened because a bulk of money shifted into it from altcoins so in this case altcoins are left on their own feet...decoupled from Bitcoin. Will this trend be continuing for the next few months? Nobody can be sure. It seems that now we are presented by Bitcoin with a big choice...its Bitcoin or altcoins nothing in between.