I believe because it is meant to cause division. It is only fair that all hear the Word of God, and make their decisions accordingly, in order for God to either justify them in faith, or condemn the for disbelief and ingratitude.
Those that are destined to perdition are set as examples to others. There is a need for this dichotomy, and I am not 100% sure why, necessarily, but a fair chance must be given to all. Thus, whether one reads the entire Bible, or hears the Word through some other medium, free choice remains, and one's heart will determine how the Words of truth resonate in one's mind.
Fools mock wisdom, and some killed the prophets and others crucified Christ. It is therefore no surprise that the mere exposure to a good or holy person, law, warning or offer, will not entice or convict everyone that hears it.