I think the game's engine could support Narrative Campaigns for single player, but due to the sheer amount of work involved, specifically recording sound FX, dialogue tracks, writing the story and dialogue, camera work and cut scenes, building 20 scenarios, etc., WFG can't put that kind of effort into making something official. We could adapt work from others, such as the Macedonian campaign, but to truly make a narrative campaign from scratch would be nigh impossible.
That's why I think some kind of Strategic Campaign or multiple Campaigns would be easier to achieve for single player. What do you think? The image above is from an aborted projects I was involved in 14-15 years ago, but is illustrative of the concept.