The reason why Bitcoin is the number one cryptocurrency is pretty simple: It was the first one. This first mover advantage persists, because Bitcoin quickly established the biggest support both from users and from developers. Having the biggest user and developer base maintains a strong network effect, that tends to draw in more users and developers, because the system appears attractive and is well-established as a payment system.
For any altcoin to compete with Bitcoin, it would have to offer something revolutionary new and useful, that can't be implemented by Bitcoin. Today's altcoins are mainly a testing ground for new ideas, that will end up being added to Bitcoin if they are good, leaving the altcoins that first introduced them behind (a current example for could be rootstock vs. ethereum).
ya.ya.yo!
Yes being the first crypto-currency ever exist is one of the best advantage of bitcoin to have more power on all other crytpo. If you have established a name in the market first the trust of the community will be in favor to you because it takes time to develop price and value and of course security for the users. Bitcoin also have more stock because the movement of its stock for the community transaction is also developing fast so the more support the more change in price happen. And as the bitcoin follows the principle of law of price and demand its price will set to increased and to pump for more businesses to be open on accepting bitcoin on their transaction.