The "why" or for what purpose, is always subjectively defined. Value, purpose, importance, significance, etc, is determined by the individual. Of course that may be based on any number of factors such as, proper nutrition, genetic abnormalities, trauma, chemical imbalances, environmental conditions, political views, belief systems, etc. Primarily you have the physical or biological system which effects the emotional system which in turn effects the psychological system which then interacts with the sociological and environmental systems. A feedback loop is created from the environment to the individual. I suppose I'm ranting.