As Hollywood puts it, it is the greatest story every told (sold?). The story attracts followers quickly and the people latch on the the emotional story and are mesmerized by it. The story has been used all over the world hundrereds and thousand of years before the Jesus story of the Christian New Testament was developed. The original story was about describing the stars and the story evolved to be a literal historical story (with Constantine's help).
The human desire for a "Superman" is so great (It's a bird. It's a plane. No, it's Superman...).
Faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings in a single bound.
Prior to the Christian Jesus of the New Testament there were many stories exactly like the current day Jesus story but with different names. The oldest known Jesus story was recorded is 2500 B.C.E. These stories were about a man that was a God and Savior for the world. He would redeem the sins of humanity by being a human sacrifice through his dieing.