You make a good point. Just to play devil's advocate, I think a Christian would say that God's plan worked since Christianity in fact took hold and spread around the world.

This is similar to saying that God created species by natural selection. Why doesn't he snap his fingers so that species pop into being fully-formed? Because he wants to create in this seemingly-natural way--despite the fact that natural selection appears to provide no opportunity for a supernatural being to help out in the process. God would be creating or planning for our salvation in ambiguous ways that can just as easily be interpreted atheistically.

Likewise, the reason God doesn't carve his name in a mountain is that he wants to preserve our freedom. He wants the evidence to be ambiguous to force us to take a leap of faith or even to disregard the contrary evidence and to choose theism out of desperation and emotion.

Whether this hiddenness of God is compatible with the idea that God expects to punish nonbelievers in Hell forever is dubious.

Moreover, Paul in Romans 1 says God's existence is "obvious" so that we're all "without excuse." In short, he and thus all the Bible-believing Christians think we're actually in the scenario in which God effectively carved his name in a mountain. The glory of the heavens testifies to God's magnificence, etc. This is also very dubious in light of the scientific overthrow of ancient anthropocentrism.