A good friend stopped writing a couple of years ago. The guy is talented, and his crime novel deserves to be published. When I'd met him about 10 years ago, he was still trying to recover from a bitter divorce. He wrote plenty of high-quality (in my opinion) noir fiction and participated actively in our writer's group. Over time he showed up less and less frequently at our group, and eventually stopped almost altogether.
So what happened? He found a girlfriend who made him happy, that's what. Life pulled him in a different direction, but love and work still left him with time to write if he wanted to. But one day he explained to me that he no longer had enough pain in his life to make him write. Anger and despair were part of his motivation to write in the first place, he said--in his novels he exacted plenty of fictional revenge on his wife, and now he feels much better.
Maybe that explains why I don't write more than I do. There is largely an absence of pain in my life. Doesn't unhappiness drive most creative writing?