Let's assume he didn't make the decision in the dark. He likely discussed it with his family. Perhaps his children are secure enough to not need whatever limited amount of income his work is likely to generate in the future. Unlike Vivian Maier, he is established and doesn't have an interesting story to fuel the production and purchase of 20 million coffee table books. He probably expects that being responsible for his archive would be more of a headache than it's worth. And likely his kids already have their own lives and don't need the added responsibility. You can't make money from an archive unless you actually push it.