I read article on photo pass that I can't find again or I would link it, but it did say that the photos are supposed to be 3/4 shots. They, in theory, don't do any full body shots, so that is why feet are cut off. Also said that they were trained to take pictures of the family, not necessarily the background, at some places.
That said, I have to imagine that it depends on the group. I know I've had pics of my son and I that include our feet. I've also stopped at several photos down Main Street, for instance, and have had different amounts of background.
After reading the article, I feel like maybe they plan it so you really have to go to every photographer to get every photo you want! But they don't bother to tell guests that! Plus, who eould actually do that?