Even though this causes a lot of people to worry, it is best as it prepares altcoins for self dependence and it also limits manipulation of altcoins
Soon enough both bitcoin and altcoins will be non dependent on one another totally
It happens like that sometimes, usually when there is a bump in the price of bitcoin the altcoins need a while to regulate and follow the price of bitcoin and if these price increase happen fast then that means that the altcoins do not get ample time to follow it so they just stay at their prices. Although most of the altcocins are dependent on the price of bitcoin, sometimes they don't follow it