I believe that they're popular mainly because well it was the first of all cryptocurrencies to be made. Honestly most of the other coins are scams and greedy ways that the developers make money. The only other coin I can think of that isn't a scam are dogecoins! What do you think?
Bitcoin is popular not only since it is pioneer in crypto currency,but also its decentralized nature due to which it is still uncontrolled by any governments and since ot works on an unmatchable secured block chain system.