Except that that’s not an actual natural law. In the same way that sometimes bad things happen to good people for no reason and with no compensation whatsoever, sometimes good things happen to people as well, whether they “deserve” it or not.

Other than that, what’s the problem with a weight loss drug? That it’s “unnatural” or “cheating nature”? The weight gain and the corresponding lifestyle and nutrition that often cause it aren’t exactly nature-given either.