The reason for that level of sucess is because it does better what it proposes to do, which is to be a good store of value and censorship resistant. Most other currencies try to do the same, but there is no way for them to achieve this being so centralized.
The reason why bitcoin is so much special than other currency is that bitcoin's price is keep on increasing unlike other currency that is not increasing and it is also become more popular to many people nowadays. Though there are some countries who banned bitcoin, but still it made the bitcoin to become popular because it will give the people a curiosity why the country is banning bitcoin and they will try to conduct some research after that so they can find the answer to their unanswered questions.