Unfortunately for bitcoin there is no ground breaking reason why BTC has to be the leading crypto, it just happened to be the first and most widely known cryptocurrency out there.

Now most of the other ones "altcoins" are all based somewhat of the btc blockchain tech. And some of these may even be better than BTC in terms of efficiency and security. But like many have stated here, BTC is the most known crypto out there by far. Hence the only reason of why BTC has to be the one is that it is widely known by the mass and have been somewhat accepted as a payment system in some areas of the world.

But to simplify the thinking, we could think of blockchain tech as the "internet" and btc as the browsers. BTC could be like "internet explorer" but who knows in the future? just like "IE" kinda died out there are new faster more efficient browsers like chrome, firefox etc.