The book "Why Does He Do That?" by Lundy Bancroft is written to help women and others understand the minds of angry and controlling men, especially abusive men. It aims to equip readers with the knowledge to recognize early warning signs of abuse, understand the nature of abusive thinking, debunk myths about abusers, identify different personality types of abusers, and learn how to protect themselves and safely escape abusive relationships. The book is meant to provide insight and empowerment to those affected by abuse through a counselor's expert knowledge of abusers' psychology.
If the question refers more generally to why people write books, common reasons include having an unshakeable idea, wanting to pass on knowledge or experience, loving to write, seeking to make a name for oneself, wanting to leave a legacy, overcoming personal challenges, or the desire to share stories or ideas that matter. Writing a book can also help the author learn about themselves, grow in character, and create something lasting.
So, for the book "Why Does He Do That?" specifically, the author wrote it to shed light on and address abusive behavior, helping victims understand and manage their situations. More generally, people write books for many deeply meaningful and personal reasons.