Would it be save to say that they flee to this as a way to avoid the forensic nature of Justification?
(Not that the ancient, patristic, and biblical doctrine of Christus Victor is wrong, but that it cannot safely be divorced from the forensic model. This is the kind of thing we often see when people proclaim a false doctrine, viz. that they make absolute another doctrine which they embrace as a cover.)
NT Wright has claimed (in What St. Paul Really Said, I think, but it might have been Paul: In Fresh Perspective) that by putting defeat of the powers at the center of our thinking about Christ's work, we are able to retain everything else. It seems to me that the Reformed, correctly, put Christ's priestly work at the center, and that this does a much better job of retaining and making sense of the aspect of the victory over the powers.
I was thinking more about this and the idea came to me: does N.T. Wright and other NPP hold to Christus Victor—and thus tone down the penal substitution aspect of the Cross—because of they're denial of the imputed righteousness of Christ? In other words, they must deny the imputation of our sins to Christ, since they deny the imputation of His righteousness to us.