The main factor for me to join a story is whether the plot and setting are interesting to me. You can have an amazing set of rules and a highly detailed prologue, but if the story is about being a traveling insurance salesman in Arizona, I would probably skip it.

The way that I see it is that the prologue is used as a sample of what you can expect in the story, sort of a hook to draw prospective players in and get them interested and enthusiastic about the story. A Storycrafter who doesn’t bother with a prologue, or only types in one or two sentences, is probably not dedicated enough to actually run the story.