Perhaps they believe that gaining the necessary amount of public attention and support requires these things to be revealed slowly and to consume many news cycles. I would argue that the pace things have been proceeding at has been perfect for those who generally don't pay attention to get a sense of how important an issue this is.
If this had all been released at once, it would have been much easier to sweep under the rug, and those who generally reflexively defend their political parties might not have had to really confront the issue. They could be proceeding this way secure a better chance of victory.
