Although God’s motives for what He does and His ultimate plan are far beyond our comprehension (eg explaining the nuances of nuclear fusion to an ant)I suspect the reason God does not reveal Himself with 100% certainty is because faith in Christ is necessary for salvation and blatant facts take no faith to believe. That’s basically the premise behind the “read the book and you’re damned” theme.
Perhaps God sees fit to reveal small portions of the greater plan to specific people (such as revealing Hell to an atheist and then reviving them) in order to aid people’s struggling faith? Whatever reason it is, I’m sure it’s much more complex and intricate than one could possibly understand.
Blatant facts can also be rejected. There are multiple ways to dismiss actual facts.
Thomas is an example. The fact was Jesus did rise from the dead, and that the others saw Him. Thomas dismissed those facts. Via rationalization and rejecting the language, the presenter, the way it’s presented, the methodology, how the facts were obtained, etc you can reject facts a whole host of ways.