Once and for all, the ship did drop its port anchor. There are plenty of photos that show this conclusively. Also a ship that is the length of over 3 football fields and, fully loaded, weighs over 150k tons, going about 8 knots, and has lost propulsion can easily take out almost anything in its way.
I heard a caller to a conservative radio program on the morning of the bridge collapse. He identified himself as a retired Naval officer. He said dropping the anchor would not have helped in this case because the sea floor there is just sand, no gripping power.