Why should fire extinguishers containing carbon dioxide not be used on magnesium fires?

As the title states, why should $$\ce{CO2}$$ fire extinguishers containing carbon dioxide not be used on fires with magnesium metal?

I understand that $$\ce{CO2}$$ extinguishers work by displacing oxygen, a crucial component of a fire. Does this somehow not work when magnesium is involved, or is there another reason?

$$\ce{2Mg(s) + CO2(g) -> 2MgO(s) + C(s)}$$