So long as we're ignoring actual throw weight to orbit, why not put just put it on Minotaur? It'd be even cheaper. In the real world, even expendable falcon 9 would require recertificating the whole thing, and probably since weight savings-neither of these are cheap. SpaceX could've done NASA certification to refly dragon on supply missions, but decided to not bother and use them for dragonlab free-flyer missions instead. Nobody has ordered any dragonlab missions, so they're sat in a warehouse.