I heard that his writing could have been a way to process what he went through during the war. That could explain the darkness.

There is a modern fantasy writer that writes quite dark stories. I read that this is because of a very sick family member, and some of his best books have been written in a hospital room. While I applaude both for turning something bad into something good, these sort of books are just not my cup of tea. And I think a lot of people are like me. We read books to get away from the problems of real life, not dive into other people's troubled minds.