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?
Judging from what is happening these days, bitcoin is so popular that it has a lot of investors who are willing to wait and earn despite any forks period that it may encounter, not to mention the fact that there are helpful websites now which helps people educate themselves about cryptocurrencies, such as
https://daneel.io/.