they continue to expand our inventories in new ways every so many patches.
They upped inventory space with a housing "bank" storing housing items, freeing up space.

They upped or inventory/armory chest space with this expansion.

They upped our inventory again with the chocobo saddle bag.

They upped the extra retainer in heavensward.

and im pretty sure there was another that im forgetting, but oh well, maybe im wrong.
(EDIT: Changing currencies to key items to free up space)