I think part of the reason is because our lives are so "noisy." We make our lives so busy that we don't have time to sit down and contemplate the bigger picture of life. Not only are they busy, but we have information overload, because we are busy with smart phones and iPods and we just don't have the silence for contemplation that people throughout history have enjoyed. This is part of the point Pete Lowman is making in this article: If There Really Is a God, Why Don't People Notice? - A Media Studies Approach.
It is an extraordinary thing. For the vast majority of the human race, the existence of the supernatural is something self-evident - even if they can't go quite as far as David's outburst, `The heavens declare the glory of God'. But we are westerners, and we live in a freakish moment of human history where, for the first time, that fundamental intuition and consciousness has somehow been lost. Only, it must be said, in a small proportion of the human race, even today - mostly living in Europe and north America (and even in these areas, opinion polls repeatedly show that, when pressed, most people still sense the existence of some sort of deity). Practically, however, our society functions in a way that denies or ignores that awareness. And, because we control the bulk of the world's media and educational resources, we are rapidly exporting our own deafness to the rest of the race. But if (as Jesus taught) the most fundamental decision in any person's existence is how to respond to God's claims on them, then this is an exceedingly serious matter.
But how has the situation arisen? If there is a God, how have we lost the sense of His presence? How have we become deaf to an intuition that, for most of history and for most of the two-thirds world even today, has been so self-evident?
Sociologist Alan Gilbert, in his book The Making of Post-Christian Britain, makes the interesting observation that it is not intellectual objections to Christianity that have caused it to be neglected. In the last century, indeed, there were furious intellectual assaults on the faith; and today there is still the occasional skirmish (often when a paperback writer is in need of notoriety). But these brief skirmishes seem to pass almost unnoticed by most people. Rather, as Gilbert says, the difficulty for Christianity today seems to lie `not in challenges to the truth of its dogmas, but in the fact that... people in a secular culture have become increasingly "tone-deaf" to any orchestration of those dogmas.' And he cites the great German sociologist Max Weber: `I am a-musical so far as religion is concerned.'