Maybe because the word Earth is used? If there were other earths how would we keep track of the earths that life looks nothing like us? Earths would all be the same. Nothing else but earth is specifically discussed for God's image.
Yes, we live on Earth, this is our story, and our God given guide lines.
It does not discuss life elsewhere, but does not deny it either.
Life elsewhere may look like us, or it may be very different from what mankind thinks it understands, it is not for me to say.