That's an interesting question actually. And one can apply the same question to Steemit. Why not use BitShares? But I guess not. It's good for a project and their developers to have the flexibility to play with their brainchild.
But I think, a somewhat middle approach can be adapted. Such as, putting an integrated DEX layer to BitShares platform that converts WAGE to your favorite Coin on spot rates. I think this would be a very cool feature to have in place. Thanks