Whizbang Dustyboots
Gnometown Hero
A swordmage is part of a distinct tradition of magic that incorporates martial techniques to create effects difficult to duplicate by other magical traditions.I mean, all classes apart from the 'core three' have a story behind them. A paladin has sworn an oath and gains their power from it. A cleric follows a god and is powered by their faith. A ranger protects civilisation from the wilderness.
Some of these are more loose from others, but they're all there. For a gish class, there needs to be more than 'this guy can swing a sword and cast a spell' as their entire class background.