The market tells us they are worth something, why fix something that's not broken?
Because to most people it is broken, if they just let us put materia in U/U gear, crafted items would still be valuable because people would be more willing to risk them than a U/U piece. It's like the sentinel's body it's a great piece but you're never going to see one with 4 materia on it. However a crafted piece we probably will because they're much cheaper and easier to come by.

I think it's the best compromise personally.