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?
Well for starters, Bitcoin's been around the longest so obviously, it's gained a lot of attention. The value of Bitcoin has massively and rapidly increased due to which it's always the talk of every town.