People no longer live in large wild settings, but amid malls and freeways. The ancients believed that the earth was the center of the cosmos. We believe that we are. There is little to suggest otherwise in manicured suburbs and cities where the sirens will be howling at all hours. It is an empty world that begets philosophically empty thinking.
Without the sense of being small in a large universe, and perhaps not even very important, the question arises, “Is this all there is?” and the answer appears to be “Yes.” Without the awe and wonder and mystery of a larger cosmos, existence reduces to blowing smog, competitive acquisition of consumer goods, and vapid television with laugh tracks. We focus on efficiency, production, and the material because they are all we have. It is not particularly satisfying, and so we are not particularly satisfied.
I suspect that the decline of religion stems less from the advance of scientific knowledge than from the difficulty of discerning the transcendent in a parking lot. Certainly the scientific has generally replaced the religious mode of thought, even in people who believe themselves to be Christians. For example, it is amusing to hear them saying that the parting of the Red Sea refers to diminution of water by a wind in what was essentially a swamp.
That is, God is all-powerful, but only to the extent that he behaves consistently with the prevailing weather.
Yet note the decline of even non-religious contemplation of such matters as meaning and purpose, right and wrong, ultimate good, and so on. It is not that people behave worse without faith, but that they cannot explain why they do not. The use of the sciences as a substitute for belief in God or gods has produced a religion that cannot ask the questions central to religion.