Over the years, I have noticed that every time Bitcoin's price goes down other alt coins follow suite. And When the price of bitcoin increases, it’s expected that altcoins go up in price shortly after. .
Bitcoin is the first digital currency and if not for anything that should be the first reason why it need to be the lead over all over cryptocurrencies, take a look at the value and price, here you could deduce how high the difference is compared to other cryptos, if you take a look at most of the investor, they have bitcoin as thier main focus coin to invest, they do this in other to play safe with their entire investment from crashing with altcoins.