Pretty sure this is a SE thing because no other company does this, makes you pay monthly for storage. Most F2P games its just a one time payment to unlock inventory space not a monthly recurring charge.
Been playing FFXIV actually totally out of space since I only have the 2 free retainers, have all the jobs and crafts leveled didn't want to pay the $2 a month for more space. In FFXI though it really isn't much of a problem for me I still have a mostly empty mog safe 2, and 1/3rd full mog wardrobe and an empty mog wardrobe 2.