Movie-making is big business. It is expensive, arguably the most expensive art form. In contrast, literature is, arguably, the least expensive art form. All that is needed to create a literary work is a pen and paper. Literature can be, and normally is, produced by a single writer, who needs to secure no approval outside of his or her own. Film is produced in a very di›erent way.
Cahir, Linda Costanzo. Literature into Film : Theory and Practical Approaches, McFarland & Company, Incorporated Publishers, 2006.