No, it is because they are part of the Port, which is a "Group Master". You cannot have nested "Group Masters".
Remember, a "Group Master" is a collection of desparate object types. As an example, using Dux's question. If you named a AAA Factory, a aaa factory type, then the AAA at the factory will not work, as the server assumes all the objects are aaa factory types.
As a "Group Master" the server will see all the different types of objects on the tile and make the appropriate disctinction on what needs to happen. Firing aaa, keeping the country strat percentages correct and so on.