Why does the New American Bible not use quotation marks for divine speech?

I have the 2012 edition of the New American Bible published by Catholic Bible Press. It's rather interesting in that there are no quotation marks when God speaks, but there are quotation marks for human speech. For instance Genesis 1:3 says > Then God said: Let there be light, and there was light. whereas Exodus 3:11 reads > But Moses said to God, "Who am I that I should go to Pharaoh and bring the Israelites out of Egypt?" The juxtaposition is especially striking in passages such as Exodus 3 wherein there is a dialogue between God and a man. I'm curious what the reason for this is. In the New Testament however they do include quotation marks, for instance in John 12:28 > ...Then a voice came from heaven, "I have glorified it and will glorify it again."