Once again, I have to say that it's a mystery. My own family life was happy to the point of flatness. I was a much-loved only child, with kind and loving parents. But human beings for the most part live their lives within a context of family, and so if you're going to write about people, you have to write about families. That's where the pain is, the conflict, the guilt, as well as the redemption.
Family is the binding fiber of human experience.
I could be reading about a thousand people consumed by flood, but if my daughter suddenly cried out, all of that would vanish, and the world would be no larger than the space that separated us. I never wanted to write about an English major overwhelmed by suburban angst, or some psycho who is so far outside the normal range of human experience that it is more or less like recording the daily activities of a shark. Family provides that human connection, and keeps characters grounded in a recognizable world. You split your time between New York City and Cape Cod. I have an office that is separate from the house on Cape Cod, although by only a matter of yards.