Worldview Necessities
If we have an “empty” metaphysic, then there’s no object of epistemology (nothing to know anything about). As ethics entails knowledge of normative statements, it also falls apart (as there is no knowledge). In-fact there’s nothing at all!
If however there’s something in our metaphysic to have knowledge about and someone to possess knowledge, but our epistemology makes knowledge impossible, then ethics falls apart (again no knowledge).
So, for there to be ethics, there must be coherent metaphysics and coherent epistemology.