1 Cor. 2:7 - NWT`s "sacred secret"

A book which examines most twentieth century English versions of the Bible: So Many Versions? (SMV), by trinitarian Bible scholars Dr. S. Kubo and Dr. W. Albrecht provides a page and a half of what it calls "peculiar translations" (pp. 108-109) by the NWT. Many of these "peculiar translations" are comparable to translations found in more popular Bibles of Christendom. But these comparable renderings are not criticized at all in SMV's critique of them.

One of these "peculiar translations" is of 1 Cor. 2:7:

1 Cor. 2:7 - NWT`s "sacred secret" vs. (according to SMV ) RSV's "mystery." Examine NIV, NEB, TEV, and GNB. But above all, look at the RSV, 2nd ed., 1971. This was the current edition of the RSV at the time this edition of SMV was written (see review on p. 58). And yet, in spite of the fact that SMV claims to compare the NWT's "peculiar" translation here with the RSV's, we find that the RSV, 2nd ed., 1971, actually says, "We impart a secret and hidden wisdom of God" and not "mystery" as SMV claims! And even the earlier 1946 RSV version reads the same! And the 1989 New Revised Standard Version (NRSV) still has "God's wisdom, secret and hidden" !

Notice what the word actually means:

"In the N[ew] T[estament] mysterion signifies a secret which is being, or even has been, revealed, which is also divine in scope, and needs to be made known by God to men". - New Bible Dictionary, 2nd ed., p. 805, Tyndale House Publishers, 1984. (Also see the MINOR study paper.)

Now, I ask you, why shouldn't the NWT translate mysterion as "sacred secret" when it actually means "divine secret"?