It's all about btc price.Now the btc price is stable so that's why I think the altcoins price is dump now.When btc price is start dumping then the altcoins price is boom again. 
They are always doing this. From the very first day of development of bitcoin, these people started the monopoly and till now we people are being gamed by them. They are whales, have got extreme hold of the market. But one thing to be understood, they can control market, not the bitcoin. They can only manipulate the price that differs from buyers and sellers.