Even before the development of bitcoin some type of digital transactions were taking place, but none of them gained this type of recognition as bitcoin. This really is all because of the distributing that happened with no marketing via media or any other platforms. Second is the development it's achieved in a very smaller period of time.
In my opinion all it is due to the fact that it is simple and easy to be used and providing more chances to be rich in very short time, it saves time and make us able to earn some extra with our regular job and those who are deprived of a regular job it is letting them to meet their financial needs easily and make their living standard good. All these are reasons for its popularity