It's something you don't really question after you handle enough roleplaying game books. In many RPG publications, preceding the often clunky "What is a Roleplaying Game?" section, you're greeted with a few pages of prose fiction. Sometimes it's a single page, sometimes it drags on interminably. The idea is obvious enough: giving players a taste of the game, its setting, its tone, and the kinds of stories it "should" tell.
But is that opening barrage of prose fiction really necessary? Is it even counterintuitive?
For a start, it's hard to generalize. The Call of Cthulhu 6th edition core book reprints the titular H.P. Lovecraft story before delving into mechanics for the author's stable of otherworldly creatures and how players interact with them.