My guess is because they are such famous books. They really hit it off and were so popular they turned it into books. You don't have to take my word for it. It's just a guess. Sorry if this wasn't the answer you wanted.
J.K. Rowling's books, starting with "Harry Potter and the Philosopher's Stone," became movies after Warner Bros. acquired the film rights and began the process of adapting them for the screen. The success of the books combined with a dedicated fan base contributed to the decision to turn them into a movie franchise.
reading books
JK Rowling's books were published by Bloomsbury in the UK, Scholastic in the US and Raincoast in Canada.
yes she did a little bit
This may be wrong but I am quite sure they both died before the books were published
no she was a singer
Jane Austen, I think
27th July 1993 ;-) she is jk rowlings oldest child
J.K. Rowling has blue eyes.
yes there is
Joann Kathleen Rowling
Eight movies. The main series has seven books; one movie was made for each of the first six books, the last book was split into two movies.
Albus Dumbledore