Is because the name "Bitcoin" is the best name for a crypto-currency.
No other name will be as good.
I think people will always find a cooler name than bitcoin, but the reason why Bitcoin is number one because of being the pioneer of cryptocurrency and being adopted by majority of population of cryptocurrency. And that is also the reason why Bitcoin is almost the best name for cryptocurrency.
yahoo was also a big player in search engines.
and then google pops up...
Google popped up and took lead of all other search engines. Google opted everything that Yahoo can't. With bitcoin everything is possible than the other digital currencies, so something dominating bitcoin is really impossible.