Readers respond to books, not just promotions.
Even when two ebooks are shown to similar audiences, their results may differ because of factors such as cover design, title, description, genre, reviews, price, retailer availability, author recognition, and series position.
Reader interest can also vary within a genre. A broad category such as mystery or romance contains many different subgenres, themes, settings, and reading preferences.
For that reason, it is normal for promotion results to vary significantly from one book to another.