She wants to be a mainstream novelist

I wonder why.  After writing the immortal Harry Potter books, why would anyone want to write mainstream novels?  We can understand that perhaps she has written all that needs to be written about Harry, and she wants to try something new, but why mainstream novels?  They have been boring and unreadable ever since Hemingway died.  The modern writers who made a real mark are fantasy writers, J.R.R. Tolkien, C.S. Lewis, Philip Pullman, Rick Riordan, Brian Jacques, or science fiction writers like Robert A. Heinlein or Tom Clancy.  Come to think of it, J.K. Rowling made her name as a fantasy writer, as good as any. 
  Anyhow, she has a mainstream novel out, it's in the Village Bookstore now, but I didn't buy it.