A promise heard without belief behaves exactly like a promise never made, and the hearer chooses which one it becomes.
Information does nothing by itself. What converts an announcement into movement is the certainty a hearer adds to it, and that ingredient has to come from their side: belief sets the state, and the state decides whether legs move or the news gets filed.
Nothing was withheld from the generation that missed it, which is the uncomfortable part. They heard it accurately and mixed it with the conviction they already carried, so it registered as news about somebody else. The cost is a smaller life lived with the better one memorized, and no one to blame for the difference.