Maybe because JC was a great guy and a lot of people believed in what he had to say. So, in order to benefit from his fame and gain the trust of his past and potential future followers, there was a gathering a hundred or so years after his death where they chose suitable accounts of his life to include in the book called the new testament. Accounts like the ones later found in the Nag Hammadhi texts and “gnostic gospels” were excluded because they undermined the authoritiy of the church and the power of priests to be the only ones to interpret the will of God.