When that guy writes about something mundane like making breakfast one morning, it turns into a series of at least 3 books.
The thing about "My Struggle" is that he wrote about his personal life, wife, friends, people he had met and it was often a bit personal, so he upset some people. He wrote about such personal things and shared so many details from his life. And he was so absorbed with the writing that his wife went through a depression and was hospitalized for a while, it turned into at big thing.