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?
How about etherium? have you seen the 1 year chart of it? Take a look and see that there is not much volatility in its growth(as compared to other altcoin).