Imho the main reason - Bitcoin is the most famous cryptocurrency. Even people which are far from all of this blockchain stuff, know what is it. It's maybe not the most perpective or workable, but it's the face of all cryptocurrency-sphere.
I am not so sure that his main power is in his fame. I am actually seeing a lot of speculation in the current "power" of bitcoin, and I would not be surprised if this inflationary bubble ends up bursting sooner or later.
Bitcoin's main power (according to me) lies in the fact that it offers people a decentralized solution that can be used to store wealth outside the traditional banking system. Gold functions as decentralized asset as well, but severely lacks in a direct comparison to its digital competitor (Bitcoin). If you look at how small the number of people actually using Bitcoin is, then you'll quickly realize that there is a huge potential growth to gain in the coming years, as Bitcoin serves a real purpose.