I don't remember Microsoft ever really giving the public a reason for canceling it. It just seemed to disappear with everyone just speculating what the reason was. Was there a press release that I missed?
I vaguely recall something being posted to the blog. I doubt the blog is still up. I could google around and check the Wayback Machine and so forth, but it would probably be faster if you did it yourself. I don’t have any inside info, I’m afraid.