A Tree is Nice . . . but the book is not

I picked up A Tree is Nice at the library because it had a Caldecott Medal. Having read it several times, I fail to see what literary merit the judges saw in the book. The author picked a great theme: accessible to children and important for society. Yet I was completely unimpressed with the literary quality of the book. The language is simple, but not poetic - to the point of being very repetitive. There are no clever twists of plot, because there isn't a plot.

So, for those who haven't read it: Don't worry; you haven't missed anything. For those who have: Can you help me see why it got a Caldecott?