* Carbon dioxide is already at its highest oxidation state. Carbon in CO2 has an oxidation state of +4, which is its maximum. It cannot be oxidized further.
* Oxygen is a very strong oxidizing agent. It tends to pull electrons away from other elements. Since carbon in CO2 is already fully oxidized, there's no opportunity for oxygen to oxidize it further.
Therefore, no reaction occurs between carbon dioxide and oxygen under normal conditions.
