Because they don't want to. It means they would lose money. GW2 did it ages ago, but "spaghetti code" in FFXIV for 10 years... sure.
Same reason they don't fix plates or the glamour dresser. How hard would it be to remove that silly, bothersome feature and just do it the way WoW does it. You get the gear, you can glamour it. We say glamour is the endgame, yet we are stuck with a piece of furniture which can only store 400 pieces of gear and every patch we get over 25 new items. GG S-E.