Because she's not moving. Duh.
You might want to read carefully before you "duh" people. This is from the presstitute's purported explanation, reproduced above:
"Look carefully at the wall from that marine's head up to the top of the frame and you will see the blurred cable that was in motion because the dancer was moving it as she spoke to the marines."
I particularly invite your attention to the words, "because the dancer was moving."
That leaves me with my question unanswered: If the cord is blurred because the girl was moving, how come the girl isn't blurred?