A carnival company guy ( who may or may not be a hack) just said it was for passenger safety on CNN. Apparently the boat can now see land but it might be another 8 to 10 hours before it docks because the boat is being pushed and pulled at 1 mile an hour.
When we disembarked the gangplank is to a stable concrete structure, where the ship is in standing water and lashed to the pier with what seemed like an inordinate amount of 6inch diameter ropes. My understanding is that the carnival ship is also " leaning" somewhat due to the wind. Getting something to safely and quickly move 3000 people from one propulsion impaired and potentially listing ship to another is not something I think any line would have a contingency for or would even attempt.
It is clear that Carnival is going to get sued by someone, right now although it is unpleasant it seems that those with health problems were already moved and this is a matter of inconvenience. If carnival tried this ship to ship transfer and, god forbid, something happened to the gangplank and it dumped passesngers into the bay between the two ships and some drowned, it would likely be the end of carnival cruise lines as anyone know it.