As we all know it when bitcoin price goes down, most of the coins are heading down too. That's because bitcoin it is the Heart of all coins if its sound then all of the coins are good, if it's Bad then all of the coins are going down too. most of the time other coins are following the bitcoin price. just look up the market right now.
That is what happen in the crptocurrency world, anything that happen to Bitcoin always affecting another altcoins.
I can't really sure what makes that to happen, perhaps that because bitcoin is the first cryptocurrency, and the other altcoin is tend to follow bitcoin's footstep.