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?
You are right on your statements, Bitcoins was the first cryptocurrency to be made and it is also the highest priced coin in the market that's why it is popular. Social media's are spreading the news and because of that, There are more and more investors are keep on coming to invest on the market.