Because Bitcoin is first coin in this market so It introduced to us about blockchain and these stuffs. Also a lot of people used to bitcoin for some reasons in the world like in China, Venezuela.
yeah sure i agree with you, countries like Japan have also legalized bitcoin to serve as a means of payment and there are some companies in Japan that pay their workers salaries in bitcoin, when you mention crypto currency or digital currency, bitcoin comes to mind, all these makes it superior.