Bitcoin is number one crypto currency in the world and not only that its market value is higher than any other crypto currency in the crypto currency market, Bitcoin is equally the only market mover in the crypto currency market when you compared to other crypto currency.
If in my opinion, Bitcoin is number 1 in terms of Store of Value. Every service is in money transfer, Convenience, Security, Investment and others because all of these things are in Bitcoin. We all know that bitcoin is most popular when it comes in investment. Surely everyone will pick the most popular cryptocurrency so bitcoin becomes number 1.
I also say it's because the bitcoin market is on top. Since most of the transaction traffic is always made with trading, and much of Bitcoin's spending is really through Bitpay or any other proxy, which is very bad for Bitcoin adoption. There is still plenty of time for new things like Lightning Network before adopting real sellers to start around the world, and there are other factors such as volatility and legalization that prevent cryptocurrency from being used as a medium of exchange. Rather it will launch their own real scalability solution, Bitcoin will probably be number one here as well.