Lucas does not seem to take kindly to suggestions. This reminds me of the whole Phantom Edit thing. He was going to be featured on Entertainment Tonight, and Lucas pre-empted that with last-minute Episode II footage. If you listen to the Phantom Edit commentary, you can hear that he is trying to reach out to Lucas and offer his services. Then listen to the commentary on Attack of the Phantom, and you'll notice a definite change in tone. He's bitter, critical, and almost resentful. I've always assumed that something happened between the scenes, along the lines of Lucas' lawyers coming down on him like a ton of bricks.
And let's not forget Lucas' recent letter to the fan club members: "I know that some of you haven't liked every single thing that I've done with the saga, and that you have a strong sense of ownership over all things Star Wars. But take that passion and devotion and channel it into a creative project of your own."