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 not popular because it the first cryptocurrency what make it popular is because it give a lot of opportunity online can be use in different platform and you can earn it for free