Yes, I know your mouth is hanging open at the moment because we just got 80 new inventory spaces. But the truth of the matter is that before the new Mog Case was introduced we already needed more than 80 inventory spaces. The is just so much stuff for us to get and hold and 80 simply just wasn't enough. 160 spaces extra would be barely enough, but 240-360 spaces would better approach reality.
Like this thread if your inventory is already full and you need more space.