Carnival has sailed over half a dozen cruise ships out of NY seasonally. At least three times they have had ships sail year round. While NCL and Royal are more….dedicated (shall we say), Carnival concentrates more on breadth of home ports as opposed to dedicated ships. The ports are limited for colder months (cannot go north, Bermuda is out, cold days of travel south (at least two each way), rough seas, etc, etc.. Way more lines follow this plan as opposed to year round.