Maybe we just make moral judgments, and we don't have theories about their nature and origin. We can imagine someone wanting to deny that an interesting debate can be cast, say, in terms of whether there are moral 'facts' or 'truths'. The categories of belief and desire are hardly ones invented by philosophers. Surely that would be an extravagant conclusion. But if that issue is a genuine one then the metaphysical questions are not so far away.
Moral realists offer an answer.
Blackburn offers an answer. Kantians offer an answer. But Dworkin does not see the question. There is somehow nothing to be explained. But this is just to ignore the philosophy.