wouldn't it make sense to use the video game footage to create a TF movie,that gets sold direct to DVD. referring to various TF video games like WFC.

They could do like what Surf's Up did. Rather then animated each scene from scratch, the designers completely built out the entire world like a video game would, then filmed where they wanted within that word so they could get multiple shots very quickly once they queued up the scene action. But that was a monumental task. Most games regardless of quality are paper thin surface deep. Ever fall through a floor? See all that void and weird geometry angles? Thats because your not supposed to be there, they only build what they think theyll need and rarely any more because development funds/time is so precious. To "simply" re-program the game's camera system to film wherever you want would lead to limited shots because a lot of it would be unusable.