Well, aside from the obvious that they're more players in Limsa because you have non homeowners as well, everything in Limsa is together in one place. If I'm not mistaken they're more MBs in a 30 person ward than there are in major city, and somehow the junkmonger, material supplier and other NPCs aren't near any of them.

If there were one central place in each ward with two marketboards, and all the NPCs that you could teleport to directly from your house I think you would see more people.

Aside from that it's not surprising. My neighborhood is a lot of single professionals and not a lot of kids and I hardly ever see anyone aside from the occasional dog walker when I watering the grass or doing something outside. People have other things they're doing away from home.