Because it is visible, measurable, shared - the culture war is easy to discuss - and Christians have lost the culture war. Christianity is not just excluded from the public realm - it is under prolonged siege.
But that is not the crux - it is the spiritual war which matter. Christians are losing that too - so far as can be measured; but it is much harder for the Enemy to win the spiritual war than the culture war. The reason is that if the culture war becomes to obvious, then the spiritual war will re-ignite.
If the culture war leads to a more primal, direct form of human experience; if people are brought face to face with the human condition (instead of experiencing it mainly via the mass media); if conflict becomes genuine rather than sham, manipulated; if dissent and protest becomes heart-felt rather than media-generated, AstroTurf-contrived, and a lifestyle expression... any and all such things will bring the spiritual war into the open - and the position of the Enemy will be exposed.
The Enemy does not merely want to make people miserable; the intention is to induce people to actively to reject salvation and chose damnation. So far, in this virtual world of sullen comfort, they are winning - and have probably gone further towards victory than at any time in human history.
But if the Enemy goes too far, or too fast, or comes into the open - then they will lose ground.
In winning the culture war, they may lose the spiritual war.
Whatever has happened in culture; we must keep fighting the spiritual war; and be ready to counter attack.