it's the first cryptocurrency using blockchain and it's promoted by the OGs as well. it's not surprising it's been the most popular. some altcoins are popular as well like ETH but BTC is just the first and more people trust its technology and its CEO is gone making it more decentralized.

it's the top cryptocurrency that has the highest market cap too.  and now that even the mainstream media is now broadcasting its worth, it will be a lot more well known and its price also might be flash on TV everyday.