^ Presumably he knows too many Starfleet secrets to just be handed over in such a manner. ... But I don't care how brilliant you and your buddies are, if you're starting out from scratch on a deserted planet, even if you do know how to build spaceships and can preserve that knowledge, it'd still take generations and generations to create a population large enough to build the necessary foundries, factories, mines and computers necessary to make a ship. Based on what we saw of augments on Enterprise, that level of cooperation would be extremely difficult for Khan and his pals. If their descendants ever did succeed in rebuilding space flight, they'd almost certainly be an entirely different race from the one originally marooned.