And why? Because despite their fine words, and their closely-guarded self-images, the actual and real ruling principle of their lives and their theology is fear, not love.
Everything flows from that original orientation, that original choice (because it is, finally, a choice). For them, to be inclusive is to expose themselves to what they fear; and what they fear most is summarized in their mythology of hell and eternal damnation: an eternal torture of body, mind, soul and spirit administered by an angry, vengeful, psychopathic god. It is all pure projection.
(h/t to Angelos)