Check out this awesome circular rationale:
“Why are we bringing it back?” asked Bishop Nicholas A. DiMarzio of Brooklyn, who has embraced the move. “Because there is sin in the world.”
I hadn't realized that it was actually John Paul II that brought them back (in 2000), but it is Benedict who is really opening the gate further. I suppose this is no surprise, given Cardinal Ratzinger's rep as a conservative traditionalist, and his pre-papacy role being something akin to a 'doctrine whip '.