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?
Yes, the biggest influence on bitcoin is that it is the oldest cryptocurrency and it has gained a lot of confidence. But cryptocurrency like ethereum, has also gained an important spot in this business. This is why investment projects like propthereum.io use it!
Agree, bitcoin have a high influence into crypto currency industry, otherwise bitcoin was also popular due to good connection of this coin to the users. Therefore, more people love bitcoin because their price in the market was continuously raising up so they trust to the credibility of this coin together with their potential in the market.
Even though bitcoin value in the market strongly raising up still more people are continuously patronizing this crypto. It is because they are confident that their price in the market still growing up.