Because AI may understand what the other book or author is useful for better than it understands yours. That does not mean their work is better. It may mean their ideas are easier to connect to the exact question the reader is asking.
AI tries to match the question with books, authors, or ideas it can connect to that subject. There is no one public formula for every AI system. So make your work's subject, purpose, and key ideas easy to understand.
See the full Authors, Books & Ideas Answer library.