Bitcoin was firstly famous due to the fact that it is a decentralised currency which means it isn't controlled by a central bank. Secondly, bitcoin allows you to trade anonymously, so people have become interested in bitcoin. Since bitcoin has become widely accepted nowadays especially after the Japan incident bitcoin has been receiving a lot of media attention. Bitcoin has also become very profitable as an investment these couple of days. These should be the main reasons for bitcoin becoming so famous these couple of years.