Why do so many book covers still use the phrase for works of fiction?

Books have used the “XYZ: A Novel” format since the 17th century, when realistic fiction started getting popular. The term “novel” was a way to distinguish these more down-to-earth stories from the fanciful “romances” that came before, says Steven Moore, author of “The Novel: An Alternative History.” Then, as now, it was a tag that identified the kind of literature you were getting yourself into.