The Batillus class supertankers built in the seventies that had a larger mass (gross tonnage) than anything now were scrapped pretty soon after since they had to sit around for lack of work. The oil crisis hit at a bad time, and it probably costs quite a lot to keep such a large ship in sailing shape. They probably were not very practical either. Out of the ten longest ship classes on list at Wikipedia, most have been scrapped already. The environment is hard. The Jahre Viking / Knock Nevis tanker that was the longest ship in the world was scrapped only recently, having been built about the same time as The Batillus class.