It's probably more trouble than it's worth from a dev standpoint. While there are positive outcomes you'd get from this, like trimming down the total item count and making the process of obtaining your sword and shield a little smoother for players, it would be a big headache to deal with. Also, one negative outcome would be that players can no longer mix and match their sword and shield glamour. Many players might prefer keeping both in the same set, but it's always nice to have the option to switch them up, and I'm sure some players inevitably do.