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?
it is because bitcoin is known and many countries and companies already embraced it. most commonly we earn so that we can use it. bitcoin can be used in most of the country around the world and can be used in having transaction even in paying bills.it is proven and legit that's why bitcoin user is increasing and is getting more popular each day.