It's not in the New Testament, but I would be more surprised if it was found in the New Testament.
The compilers of the New Testament were obviously not concerned with revealing the deepest mysteries of God (see comment for clarification), but rather, were focused on documenting the life and ministry of Jesus Christ and His Apostles.
Most of the New Testament's purpose is to show that Jesus is the Christ. This was done by the accounts of Matthew, Mark, Luke, and John. The epistles, then, mainly declare His doctrine and document the ministry of the apostles.
Abraham was shown much about the sky in vision. His communion with God as recorded in Abraham 3 is highly personal to him. It's not something that would be written in an epistle to somebody else. It's not a direct account of the life and ministry of Christ or His apostles.
As the Book of Abraham is more like a personal journal rather than a letter or biographical account, I don't see why, even if the compilers of the Bible had Abraham's manuscripts, they would choose to include it with the New Testament.
Of course, any number of answers -- mainly guesses -- could be given for why anything else isn't in the New Testament, either. Or the Old Testament. Mormons would say that because these things aren't revealed in the Bible, it validates the need for a restoration.