This is incorrect. Most cruises from the US are closed loop cruises meaning they depart and arrive back at the same port. CBP only requires a birth certificate and government issued id in these circumstances. In addition almost all countries in the western hemisphere which US originating cruises regularly visit allow US citizens arriving and departing via the cruise ship to enter with only a birth certificate and goverment id. In the Carribean the only exception which comes to mind immediately is Martinique. They used to not require a passport but changed this requirement during covid and have not gone back. Although US originating cruises do visit Martinique, I did so on a cruise in February, it is not a common destination.