I’ve known many writers who have used pen names. One already had a cozy mystery series when she sold a second series, and there was concern that sales from one would not build on the other, but rather cannibalize. Another author I know wanted to escape the tyranny of the computers, which reported falling sales for previous books. A writer known for her chick lit has donned a different last name for her middle grade novels.
I have a funny middle grade - written with a co-author - that’s about to go out in the world. If it find a home, I might use a different name.
"Like the experience of first authorship, writing under a pseudonym gives one the sense of discovering oneself by way of redefining oneself, even if it is only for the space of a single book," says Joyce Carol Oates.
An article in the Washington Post explores the many reasons authors use pen names.