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?
Like you said Bitcoin is the first of it's kind and people have more trust in it than other cryptocurrency. There are like hundreds of cryptos available and many new being created. But still BTC has 59% dominance in the crpyto capital. This shows that people are more into BTC than other cryptos. If you look at the features there are other coins that are have faster transaction rates and added features than BTC. The main reason most people only trust BTC and they are attracted to the growth in it's value.