Well, mainly because of the mother-son relationship which can roughly be rendered as Oedipal one. The mother is strong and intellectualy superior to the father who is only physically strong. She is dissastisfied and dissilusioned, and living in hard circumstances, with no support coming from her husband who should be a pillar of the family, turns to her younger son, especially after the death of the older. Her love is one that suffocates, permits no other female influence. Even when she dies, her son feel her grip over his life. He turns to lights, symbolically to freedom of her influence, away from the darkness, but still, he struggles.