Bitcoin is the world first Decentralized digital currency. Being first is always matter most. Their are other CryptoCurrency are like Dogecoin Altcoin Litecoin etc but they are not as much as famous then bitcoin. Bitcoin innovative technology makes it better then other. Another thing is its price is pretty much higher than any other CryptoCurrency and stable also. Bitcoin was declare legal in many countries  this thing boost its popularity high. Many small business owners mostly using bitcoin for trading so this thing also makes it popular among other CryptoCurrency