I don't know anything about WoW, but I do know that we've had an insight into how awkwardly the inventory system has been programmed. I know we've been told that a "fishing tackle box" is impossible without taking up inventory slots that could otherwise be used for any type of item. I know (from observation) that the "new" glamour plate system has been designed to sit over the old prism system (already, as I understand it, something added on top of the original glamourless gear system) without altering how it works in any way, and that whether in inventory or the dresser, each gear piece seems to occupy an inflexible piece of space that is difficult to expand, reorganise or collapse into something less complicated.
Even if we want multiples of the same piece in the dresser, they have to be stored as separate items with their own dye information, and I suspect each plate is actually duplicating the item again (as they are not affected if you subsequently dye the base piece or remove it from the dresser entirely).
Everything points to them working with a creaky, impractical core system that they can't easily rebuild, so they're doing the best they can to make it work, even if it still looks "not good enough" compared to better-designed systems.