Because the author needs the money…

…The New ‘Harry Potter’ Book Will Have Two Covers, And Not Just A Front And Back
LONDON – The fifth installment of the Harry Potter books will have two separate covers, one for adults and one for children.
Bloomsbury Publishers unveiled the designs Thursday. The adult edition of “Harry Potter and the Order of the Phoenix” features a somber black and white picture of a phoenix, while the children’s version of the boy wizard book is illustrated with a more vibrant red and orange bird rising from flames.
The designs will be used for editions released in Britain and other English-speaking countries, except the United States, where the book is to be published by Scholastic Children’s Books.
The latest work of author J.K. Rowling will be released around the world on June 21. Fans have waited nearly three years for the schoolboy wizard’s fifth adventure. Bookstores have already been deluged by Potter fans pre-ordering copies of the book.
Online retailer Amazon has taken more than 130,000, twice as many as were taken for the fourth book, “Harry Potter and the Goblet of Fire.” Released in July 2000, that installment sold more copies on the first weekend after publication than any other book, according to Bloomsbury.
Rowling’s four published titles have sold an estimated 192 million copies worldwide in hard and soft cover; the books have been published in at least 55 languages and distributed in more than 200 countries.