Because people act from the mind. The mind acts and reacts according to what has been placed in it. There is no natural morality in it when created. It has to be downloaded sometime early in life for it to be activated in any particular event. Only people who live by the spirit have a natural morality built in. Unfortunately, the mind needs to listen to the spirit and obey it before the body will act accordingly. The mind in most does not want to listen. It is to busy with it's music, tv, sports, toys, sex, etc... to care.