Bitcoin is mother all crypto currencies. If you follow the flow bitcoin dominates the price of all other crypto currencies. U might see ETH price is $3k or $4K but BTC price for ETH didnt cross .0.08 BTC but in the last bull run it crossed .01 BTC so price is purely determined by bitcoin only!! Yep ETH has more use cases but that doesnt mean it can overtake bitcoin and BNB is still a baby 
This is because the number of bitcoin developers is the largest compared to other platforms, early developers are wallet providers who are actively campaigning thus making bitcoin the most popular position among others, most people will look to bitcoin to assess the market or buy altcoins.