No, not every book has an illustrator.
In a book, the illustrator is usually the one who does the illustrations.
Illustrators often receive a commission for their illustrations, but it is not always clear whether or not these payments come out of the author’s royalties.
Illustrators generally earn a higher wage than non-illustrators, but the range is often quite wide.
Illustrators price their work differently depending on the market, the type of illustration, and the style of the illustration. Prices for an illustrator’s work can range from $0 to $50 per image or project.
Illustrator gets more money because they are often contracted to create illustrations for books, magazines, and other products.