This appeared on the local Computer Science opinion bboard...
I think the crucial question is not why God doesn't reveal himself to us; he may simply be too busy, creating new universes or something. Rather, why didn't he make his existence obvious from his creations? For example, he could easily have signed his creatures so that we somewhere on the animal would find something like:
Copyright © The Sixth Day, God. This animal is commanded to be fruitful and multiply. It may do so freely, provided that this copyright notice is included.
But seriously, it is inconceivable to me that a God could have played any significant role in the creation of the universe without leaving unmistakable evidence of his existence.