Here's why:

* Bond strength: The double bond in O₂ is stronger than the single bond and partial double bond in O₃. This means more energy is required to break the bonds in O₂.

* Resonance stabilization: While ozone has resonance structures, these are less stable than the single, strong double bond in O₂.

* Thermodynamic stability: The standard enthalpy of formation (ΔHf°) of O₂ is zero, while that of O₃ is positive (+142.7 kJ/mol). This indicates that O₃ is higher in energy and less stable than O₂.

In summary:

Diatomic oxygen (O₂) is more stable than ozone (O₃) due to its stronger bonds, lack of resonance structures, and lower enthalpy of formation.