Why bitcoin is getting so famous ?

Simple answer on this one: Because right now it is free money.

By mining bitcoins you get money for just letting your machines work for you.

It is safe, fast and the biggest part anonymous. Problem is that because it is anonymousmany illegal sites use it to stay off the radar of government and the public. (not talking about leak forums and such. I meanreal stuff like murder stream sides, illegal weapon markets, online drug markets and basicallyeverythingserious you can find on the darknet)