If you have notice the current bull run, at the start it's bitcoin which is pumping hard while altcoins don't follow right away, the first reaction was a dump as investors are going all in bitcoin but as the market is more bullish, slowly investors are putting their money on altcoins and that's what we are seeing now.
This means that investors are trusting more on Bitcoin and they can afford to hold it longer than these altcoins. And if we can see if there is a spike on altcoins, most of these are just hypes compare to Bitcoin that we know has sustainable market demand.