Turning your mats into gil takes time, even if you go full out undercutting everyone else you could end up with mats stuck for days up for sale, and then when you try to buy mats they might be more expensive than what you sold them for, or there might be a shortage of mats and there aren't enough for you, it's really not a reasonable alternative, and doesn't solve the current issue at hand, the fact that the game is over 2 years old and the money they got from renting retainers is not going back into solving the lack of space.

I feel like your whole argument is just "I don't have any problems, therefore this isn't a problem".