Because they cross their eyes and stick out their tongues.
They make their bottom lip all pouty.
They smile really adorably but kinda cheesy. (she's been doing this a lot the past two days when I coo and talk to her so I think it's for real)
Their heads fall on their chests.
Or off to the side.
They look really bored.
They get ready to sneeze.
They really sneeze.
They purse their lips.
They stick out their lips.
They wrinkle their brows.
They yawn and open their eyes freakishly big.
They look adorable for one single picture.
And that is why, taking photos of newborns is hard to do.