Why we add "post-" to everything

Why is it that we are so content on defining ourselves but every label so long as it as a "post-" prefix? For example one can be "postmodern" or we are told we live in a 'post-Christian' culture. David Wells has these insightful words:

"[T]he continuing need to be post is still a telling indication of the modern mind. What it tells us, I believe, is that beneath all of the difficulties and disappointments that modernity has brought, there still resides a belief in progress; we continue to think, or perhaps fervently hope, that we are still moving toward a better future. The truth of the matter is that most Americans are impatient with nay-sayers and are disinclined to indulge, or even to attempt to understand, those who think that the basis for such hope might be gone. It is not merely that Americans typically think that such arguments are wrong; more importantly, they think that these arguments are offensive. They violate an important tenet of the cultural creed--namely, that there is always hope because things are always improving, despite the fact that under secular auspices there is no truth by which one can judge whether a culture is moving forward or backward." --David Wells No Place for Truth or Whatever Happened to Evangelical Theology p.67