It would appear to be much easier to launch a small Zodiac boat to retrieve any passengers that go overboard then turn around the entire cruise ship.
On the open ocean, launching a small craft like that for a rescue would endanger everyone on it. Besides, even if you were to launch one, the cruise ship would still need to turn around to recover it. With the ship steaming away for some time before starting the rescue effort, the small craft would have a very large expanse of ocean to cover.
When I was in the Navy, one of my people went missing while we were underway. The ship was turned around at the first report of the possibility of his going overboard. We retraced our course until he was found. Fortunately, he had hidden away for a nap in a fan room rather than having gone overboard. While he was in some trouble (Captain's Mast) for doing that, things could have been much worse otherwise.