There is concrete reason for the writers to use pen names and not only one but several pen names by a single writer. Sandra Brown is known to use various names and for romantic novels she primarily uses the name of Erin St. Claire and for suspense novels she has the name of Sandra brown.
The probable reason for the writers to use pen names is that they can project a particular image for themselves and whenever people come to listen to the name of the author, they can relate it with a particular genre. Sometimes authors even use pen names to show some thing interesting aspect about their characters. We can take the example of Mark Twain. The meaning of this pen name was two fathom deep and it is to convey the idea of depth that he probably took the name.
The probable reason for the writers to use pen names is that they can project a particular image for themselves and whenever people come to listen to the name of the author, they can relate it with a particular genre. Sometimes authors even use pen names to show some thing interesting aspect about their characters. We can take the example of Mark Twain. The meaning of this pen name was two fathom deep and it is to convey the idea of depth that he probably took the name.