The canard of a "post-Christian world"

It's common to come across various types declaring we live in a "post-Christian world." This is a canard simply because God's remnant in all eras of His plan of redemption have always been numerically small, though with big influence due to the Holy Spirit and common grace and so on.

The Puritans, for instance, were a small, very small, island in a sea of unbelievers and unbelieving culture, everywhere they existed. People tend to think historically identifiable Bible-believing Christians lived in some kind of monolithic Christian culture.

It's true that the foundation of western culture and civilization is Christian to the marrow; but that is just the same as saying the Incarnation happened and changed everything. The civilization of Rome, the culture of Greece, the theocracy of the Isrealites/Jews ended. The god Pan announced the end of his fellow mythological beings.

The people who say we live in a post-Christian world stand on the foundation of and breathe Christian culture and civilization. That doesn't have to do with the number of Bible-believing Christians around today, or yesterday, or in the Middle Ages. We've always been a small number. Yet God's influence in the foundation of western civilization and culture is as central as at the beginning.

The people who say "post-Christian world" are consciously or unconsciously setting that pronouncement against a popular myth of Christendom in the middle ages, not realizing the number of Bible-believing Christians back then were most likely the same percentage (if not less) than what exist in today's population.

There's no 'post-' in "post-Christian world." The foundation we stand on is as God-influenced as anytime in the past, and the number of Bible-believing Christians is similar as anytime in the past.

So, a lingering question from what is stated above: why is Christianity so associated with 'western' civilization and culture and not eastern and so on? Western is just to say the universal dominant civilization and culture in the world since the Incarnation.