The England squad is jam-packed with talented players and Jack has had a poor season but under Southgate, one of England's biggest weaknesses is tempo control - getting stuck in turgid possession without penetration or allowing anxiety to drive everyone forward too fast without enough accuracy.
Jack is a feasible solution to both of those extremes because he's such a tidy and controlled player who knows how to apply sustained pressure and how to take the momentum away from an opponent.
If you choose the squad by listing every eligible player in order of how good their season's been then I'm not surprised that Jack doesn't make it. He's struggled for a number of reasons.
But if you look at what the squad needs, and what the other players provide, it feels silly not to take him. If he responds to the disappointment well then it'll probably end up being a good thing for him and City, but I think there'll be a point where England miss him.
On a connected note, it feels weird to me that these decisions are being made before the final friendly.