In modern life, as opposed to the miracle strewn stories of the past, we have no direct contact with anything we can call God. There are some who would disagree with this, though, and claim that they experience a true miracle or conversation with God on a frequent basis, but I certainly haven't and I think most people are like me. What then could be the reason that God, assuming he exists in some form, seems to be in hiding? Why is there no direct evidence for the existence of God?
Well, we could first deconstruct the idea of a "willing" God and suppose that God cannot choose to do anything. He didn't choose to go into hiding, he isn't really a "he" at all. Perhaps by the nature of what he is, he cannot make "himself" apparent to us.
On the flipside of this is the idea that the weakness is not in God, but in mankind. Perhaps God does act in the universe but in so transcendent and so subtle a way that our limited human minds cannot perceive it.
Perhaps it could be that the universe is too sensitive for such obvious interventions and like a soap bubble would be destroyed the moment such actions were tried. This is another argument for a "limited" transcendent God.
Perhaps God is not limited, nor transcendent in that way, but part and parcel of this universe and there are no such things as "miracles" as anything that happens at all is a function of this higher Existence Producer.
Then there are more provincial possibilities, but nonetheless worthy of mentioning:
Perhaps God is punishing humanity and leaving the world to work by itself free from Providential aid.
Perhaps God doesn't care about humanity. Either he left the universe in total or is focusing his attention on a distant part of it, but in either case allowing the world to operate on its own through disinterest.
Perhaps it is some sort of test of faith, or test of human determination, or human creation. Perhaps God needs to be absent to fulfil some mission that was planned for humanity.
Perhaps God doesn't exist as far as this question makes any sense. How can what doesn't exist hide?
I am sure there are also possible answers, but I'm just throwing these ideas out there.