I am curious as to why Google chose CC-BY as the only option for Youtube videos. I'm guessing just for ease of understanding? After all, having an option of CC

I am curious as to why Google chose CC-BY as the only option for Youtube videos. I'm guessing just for ease of understanding? After all, having an option of CC-BY-SA-NC (ShareAlike Non-Commercial) would address points 1,3 & 4 straight off the bat. At minimum, Share-Alike would be a great option to have. Flickr does a pretty solid job of this, IMHO.