The Vulture article delves deep into the potential whys. It appears he suffered serious abuse by his parents who were very prominent Scientologists, pretty much the leaders of the cult in the UK.
Then, as an adult, he refused any kind of therapy. Instead, he became an abuser himself, even going so far as to potentially traumatize his own son.
None of that excuses his behaviour. He's obviously very intelligent and his works show that he knew very well that what he did was evil and inexcusable. He wrote a chapter of Sandman about this exact thing! But in the end he just didn't care. Because he probably thinks he's rich, he's famous and the rules don't apply to him.