Why is the highest oxidation state of a metal exhibited in its oxide or fluoride only?

The oxidation state increases when an atom loses its electron. Example: When Fe loses 2 electrons, its oxidation state becomes +2 from 0.

Oxygen (O) and fluorine (F) are very strong oxidizing agents. Both oxide and fluoride ions are highly electronegative and have a very small size, so they attract the electrons from metal atoms. Hence, they oxidize the metal to its highest oxidation state.