I agree with most of the points above. Here's my addition:
In most RPGs, you have the party of PCs, all of whom are of roughly equal importance. Some may have the spotlight in one bit of the adventure, some in other bits, but overall, no one stands out.
In most successful fiction (novels, films, etc), you have one protagonist. This is the one person that the audiance most identifies with and wants to see succeed. The plot and theme most heavily revolve around the protagonist and how they change from beginning to end. That's not to say that there aren't other "main" characters, but there's still focus on that protagonist.
Example: There are a bunch of people in the Fellowship, and they all have well-developed personalities and goals, as well as plots that feature them. Frodo, however, is the protagonist, and the most important bits of plot and insight revolve around him in some way.
Thus, I think that for an rpg novel to work, it needs to be changed from "a story about a band of brave adventurers searching out the world-saving widget" to "a story about Joe, who, with a band of brave adventurers, searches out the world-saving widget, verbing noun about his own noun along the way."
Of course, there will always be exceptions, but in general, I find this to be a necessary bit of structure.