The day and age may have less to do with it than it appears at first. For one thing, the fact is that what one person can easily perceive, others cannot, and this has been true for thousands of years. (As Admiral Morison said when asked whether people in Columbus' time believed that the Earth was flat: "Some people did. Some people still do.") For another thing, what people believe and what they believed in the past, and what we are able to perceive about those beliefs, are two different things.
Thousands of years ago, in ancient Greece and Rome, where people were allowed to discuss religion openly, some people saw through it. Possibly some people saw through it much earlier than that but were prevented from expressing their insights in written form, so we never heard about them. After ancient Greece and Rome, Christianity prevented written expressions of religious skepticism, so we don't know how many people in the West were atheists in the Middle Ages and Renaissance. (We don't know of any Medieval atheists, but many Medieval theologians spent a great deal of time devising proofs of God's existence. Why would such a thing have been necessary is belief were unanimous? Against whom were those theologians arguing?) We don't know for sure how many atheists there are today because there's still some pressure to conform to religion.
There is currently an upswing in the number of people who identify as atheist. Some atheists see this and think, At last, progress is being made in people's ability to think! And I also think that some progress is being made, but I don't think we can know for sure how much of the increase in publicly-visible atheism is due to mental progress, and how much is due to a decrease in the pressure people feel to conform.
If we're really trying to understand religious belief in Western civilization (Ancient Greece, Ancient Rome, Middle Ages, Renaissance, Modernity, Now), we should entertain the possibility that all along a majority of us have been atheists, and that what has changed has been above all the degree to which we have been coerced to appear to have religious beliefs.