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.
Neat!