This is always a common factor. Anytime the price of Bitcoin increases the prices of altcoins begin to fall.
What is the explanation to this? It is a very simple explanation. People who placed buy orders for altcoins are simply pulling their orders to cash in on the Bitcoin frenzy.
Anyone who bought Bitcoin when it was $420 and noticed it has increased to $450 will do what anybody will do. Sell at $450 and make a profit. And this is the major reason for the fall in altcoins prices.
I will bet you that when the price of Bitcoin start to fall which will definitely happen , you will begin to notice a rise in price of altcoins again.
Now that coins are low. It is a good time to start buying those altcoins cheap.