It is the first cryptocurrency that battling to the local currency it is the first that struggle a lot just to be popular by now no doubt about its success, though we can't anticipate this because this currency have so much potential no doubt so many alt coin trying hard to copied it.
That is not the sole reason. If that was the case, then Litecoin should be more popular than Ethereum, since the former was invented at least 3 years earlier than the latter. But yes... being the first and "original" crypto can have its own advantages. But one reason why so many people trust BTC is that its inventor (Satoshi) never tried to profit out of his invention.