Understanding Narcissistic Personality Disorder

Narcissistic personality disorder is characterized by an inflated sense of self importance and excessive need for admiration. People who suffer from narcissistic personality disorder have less gray matter volume in a region of their brain believed to be involved with empathy. This explains why they are more focused on themselves than others. So why do narcissists lack empathy? It's starting to make more sense to me now almost like an aha moment when someone says I don't care they really do mean it.