I can certainly get behind the idea of narrative guidance, but the less focused an experience you're trying to create, the more counter-productive this can be. I'm skeptical that every game does have a platonic session. Or rather, that every game is well understood through the lens of having a platonic session, or better designed by a designer who uses that framework. There's more than one way to guide players, and I think a lot of games that don't draw the shape of a platonic session or an otherwise refined narrative guideline for players do instead draw a very detailed picture of how to use the mechanics as narrative tools on a scene-by-scene and session-by-session level.
A game of Apocalypse World or Spire probably isn't a good candidate for the platonic session lens; these are games that wrap narrative into mechanical minutiae and crowbar flavor into crevices of the system and the voice of the text and then hand players the power to obliterate anything resembling a consistent narrative structure with each new ability selected in character creation--Spire much more so than Apocalypse World, but they're both in that general direction. Games like these often have quite a bit of text dedicated to helping players use those chaotic systems effectively not by steering the session into a particular shape, but by steering the participants in the conversation into a particular frame of mind. This is by no means incompatible with what you seem to be after, I'm just not sure it's quite the same thing, either, and it doesn't seem to be an issue of missing material to me.
I can't speak to anyone else's creative process, but both as a GM and a designer, I find it very helpful to proceed with a looser sense of purpose in mind. I make the game I want to make that does what I want it to do, but when I get down to the more difficult work of testing and refining I'm not worried about a platonic session, I'm worried about providing others tools that do interesting things. I think most games lack clearer narrative guidance not just because some of them need more but because a lot of them don't. If the goal is for players to tell a very particular story, naturally it makes sense to guide players along that path very strongly. But that just isn't the goal of many, many games.