The problem with fleshing out a book that is in first person is that the narrator (or Annalist, as the case my be) must have contact with the person or someone who has had contact with that person. The Company never had contact with many of the Taken.
Also, I think that in the first series, Cook does a great job of describing "life in the trenches." How many privates in Desert Storm *really* knew what Schwarzkopf was like? To them, he was probably the sterotypical general.