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!
You have point. Being the first ever established crypto-currecy is one of the reason bitcoin power nowadays. Before we all know that bitcoin start on a low scale of demand so meaning to say that its does not a have a value before but as support of the people increased that is the time that the development of bitcoin also take place. So for me bitcoin is quite revolutionary meaning to say that it is mostly used by the people who extend for the technology because bitcoin needed the internet for it to be innovated and for it to develop more its transaction and price to have power in market and economy.