I think I know how things work in that world enough to assume that first and foremost they looked at this as a great and compelling story that would garner interest, and perhaps controversy, which would increase the interest. These things start with a pitch - a producer approaches the network with an angle on a story, (if it's a true story) and it goes from there. This being the 5 year anniversary, I am sure ABC wanted to do something "significant" (and that's a business as well as a philosophical decision) and perhaps in the end the facts speak for themselves, and "truth will out" - as they saying goes. The 9-11 Commission report I am sure, looked like a great jumping off point or hook from which to tell this story.
For what it's worth, the writer will be on Sean Hannity monday to talk about what was cut.
Since this will be shown commercial free and cost $40 million to make are they expecting to recoup that through dvd sales?