It's about man's never ending quest for knowledge. Hypothetically (read: Religiously), God gave us the faculty to reason out the universe, which we have been doing since before recorded history. We do not always do it accurately, but we always do it. If reason has allowed us deeper understanding of one thing in Creation, it makes reasonable (see what I did there?) sense that reason would allow us to understand another, and perhaps even God itself. Humanity strives, seeks, finds, but it does not yield, to paraphrase Tennyson.
The problem arises when people believe that there exists two clear sides to the matter and forces others to choose between one of the two: the True Believers with whom faith alone holds sway, and the Skeptics, who would not believe in God unless science proved God's existence without a doubt. In fact, throughout Christian history, people have been questioning God's existence not as a matter of atheism, but as a way to gain a deeper understanding of God. Aquinas, for instance. Some early church fathers believed that God could only be understood in the negative (i.e. infinite is the negative of finite) and thus could not be understood in the affirmative. On top of that, one must consider that other religions have existed throughout the history of the world, each with its own understanding of deity. In what do you have faith? Why is one faith truer than another? Lot's of people go "well, it doesn't matter which God you believe in, so long as you believe in a higher power" but the truth is, organized religions almost universally condemn the practitioners of other religions to some form of hell. And organized religions claim these condemnations come from on high. So it makes sense to go: "Well, I don't want to be sent to hell, which is the right religion? How do we know? Maybe we should find God and ask him."