Amazon has changed the way people look for books. A reader can narrow their search with a few key words and customers are very faithful to certain genres. Hence, if an author wants to write more than one type of book, today's algorithms necessitate writing under a different pen name.
Although it makes the business end of writing a little more complicated, it is very freeing to build a new persona and write with a different voice.
Even before Amazon, author's used the vehicle to write in different styles. Agatha Christie's pen name for her romances was Mary Westmacott. JK Rowling also uses a pseudonym; she writes crime fiction under the name of Robert Galbraith.
“Both Agatha Christie and JK Rowling, among others, have psuedonyms.”
Since I write children's historical fiction, Regency Romance, Cozy period mysteries and DNA Mysteries, I have created two pen names. Ann Sutton is my middle name and my maiden name and Victoria Windell is the name my mother almost gave me and her maiden name.