Removing armor from your inventory and allocating a separate data block for it every time you change gear would drastically increase system load compared to simply selecting armor from your inventory. The PS2 is already hitting its RAM limit at 160 items in a menu at a time. It would not be possible to add a third data block in RAM to hold your currently equipped gear. Not to mention the speed at which this data transfer must move is incompatible with how most people play FFXI. Instead of being able to swap to WS gear, WS, and swap back in a second, each piece of gear being moved between Data blocks would have the same latency as items being moved to/from your Mog Safe. Situational gear swapping would be impossible.