PS2 memory limitations. GobbieBag is always in memory because any drops or item pickups go there, adn you can get items from the moogle in your moghouse because of furniture. So it lists inventory in your Gobbiebag and the one other inventory of your choice. You can't load two alternate inventories simultaneously because of the listing of the Gobbiebag. A system overhaul would be needed. Every new inventory bag is also going to increase time for the inventory to load to be accessible, though removing the 56 kbps data connection limit from the game client might help that.