I actually think the evidence for God is clearer than what is claimed. However Keith Ward raises an interesting point, especially given the atheist penchant for science.
As to the question of evidence, I think that is rather like asking why we have to try so hard to discover scientific truth. Why did God not just tell us about quantum physics, and make it all obvious? There is a truth about the physical world, but it is extremely hard to discover. Part of being human is having to learn for ourselves, after taking many false paths and blind alleys, what the world is like. (Chapter 8, Why There Almost Certainly Is a God)The irony Ward identifies is remarkable. Scientific evidence is not obvious prior to the fact. But even more damning is that the scientific method was not particularly obvious. It was late on the scene and only originated in a single culture. And even now when we understand how the scientific method operates, unravelling the workings of the world takes considerable effort.
What's more, evidences for God—the design argument and the moral argument—were known about centuries before science. Many cultures understood this evidence for God for millennia; yet the scientific method, which so enamours the materialists, took a long time to be identified. Further, the development of the philosophy of God (theology) proceeded significantly while men struggled to progress in natural philosophy (science) due to their unwarranted devotion to Aristotle.
It seems that the evidence for God is indeed much more accessible to man than science.