Why would they do that? The facts over time and history is a great example is that they do NOT sell well (at least in comparison to Carnivals other markets). Add to that, the limited itineraries and we get the answer, at least the answer Carnival believes.
They like it becaus eit their STRONGEST market. I feel the same as you but 8 million people (and 3 of the 7 largest cities in the US) dictates other wise.
Never bought into the “open space” scenario. I see no problem at all in Carnival announcing a phase 2 for a new cruise port. Matter of fact, it seems like a good idea.