Reloading steel & aluminum cases is akin to casting your own bullets in one sense.Some guys collect & remelt aluminum cans into ingots. While you can resize steel & aluminum cases, there is just so much brass cases around, the extra effort seems a waste IMO.
Most reloaders buy bullets as components rather than cast their own. Where I think the similarities end is the very limited amount of reloadings available for aluminum & steel cases, whereas casting your own bullets can significantly reduce bullet costs & pay off your casting setup after as little as 2000-3000 cast bullets.