Catboys pretty much said everything I had been thinking myself. Higher profits are made when you yourself go out and obtain the items you wish to sell at the expense of time (and not everyone has the time nor patience to make money). Lots of people don't seem to understand economics either, and just undercut others for ridiculous amounts in hopes of being able to sell something without realizing the product's true cost due to time/effort in creating it, but they cut their own profits considering people will naturally buy whatever is the cheapest listed item on the marketboard.

As for your next concept, those who don't have gil either don't have much of an interest to make gil or spent it all on materia for novus lol. I can imagine some people holding onto their gil because there still really isn't anything worth spending it on at the moment in some people's eyes. I bet some are still holding out for their own personal houses. Expensive glamour doesn't appeal to everyone either.