Personally, for me, it's that I want to be able to read the full story together. Where the movie is self-contained, I wouldn't be so bothered but here we have a prequel and a sequel both building on what was in the movie. The adaptation is desirable because I can then read the whole story from start to finish.
Just read the latest issue of ongoing at last. I certainly wasn't expecting the story to go in that direction but it's fun enough if a little vague on when Vulcans became immune to heat and smoke... The story feels a bit more comic-booky, although I'm enjoying the interludes with the romulans and klingons.
Biggest grip - still no T'Pau!