Look at it this way: People are selling altcoins for BTC because they're FOMOing the current pump. They are leaving altcoins at ATLow and entering BTC near ATHigh.
What do you think it's gonna happen? The answer is obvious, people entering near all time high on BTC will get crushed and then they will come back to altcoins after they are already on the move.
Don't panic sell at the bottom, the time to sell altcoins is long gone, if you're on the loss with altcoins, hold on to it because trying to time the market is super hard (Not financial advice)