Why does the narrator give so much information about her family and background?

Scout needs to give context about setting so the rest of the book will make more sense to the reader. The first chapter's emphasis on family history and stories within stories describes the rigid social ties that hold society together in the little town of Maycomb, Alabama, and the inescapable links that tie an individual to his or her family or clan. It is through this lens that we can appreciate the American South, Maycomb in particular, and the culture that the story is set in.