When you ask 'why', you are asking 'for what purpose?', 'for what reason?' or 'to what end?' Inherent in any question of 'why' is the assumption that there is a rational intelligence behind whatever system, or set of facts the question is being asked about. For example, if you ask 'why' the sun rises every day, a scientist might (errantly) explain the various physical mechanisms and facts that we know lead to the sun rising. The scientist is really answering the question of 'how', and not 'why'. When you ask why the sun rises, you're asking for what purpose. Even asking the question implies a recognition of a will, and of an intelligence, responsible for making the sun rise. For it makes no sense to ask 'for what purpose' or 'to what end', or 'why' a random, chaotic, un-planned event happened.
If you are a naturalist, that is you believe the natural world is all that exists, then you can only rightly ask 'why' questions about human decisions. Why this person did this, or why did that guy do that. You can't coherently ask 'why' questions about any natural phenomena that occur independent of human will, for the question becomes nonsense. 'Why is the sky blue?', 'Why do earthquakes occur?', 'Why does the mockingbird sing?' Forget about being answered, none of these questions can even be asked by a naturalist. They must either be recognized as incoherent, or the 'why's must be replaced with 'how's.
Therefore it's my contention that the very fact that 'Why' questions preoccupy so much of human inquiry, probably the vast majority of it, is evidence that God exists. If we are solely the product of natural phenomena, then what evolutionary paradigm could our mental preoccupation with the nonsensical question of 'why' possibly serve? As a matter of fact, in evolutionary terms, that very preoccupation would be a quite costly, and dangerous distraction from more pertinent questions such as 'when' 'where' and' how' to secure our next meal, for example.
But if we are the product of a will, and of an intelligence, made in that image, then it follows that we would want to understand the reason behind events occuring. And that the rational being that created us would endow us with rational faculties of our own, and a curiosity to understand not only the what, where, when and how, but also the why.