Here's why:

* Ionic Bonding: Aluminum oxide is an ionic compound, meaning it's held together by strong electrostatic forces between positively charged aluminum ions (Al3+) and negatively charged oxide ions (O2-). These ions are tightly bound in a rigid lattice structure.

* Insulator in Solid Form: In its solid state, aluminum oxide is a good insulator. The ions are locked in place, preventing the flow of free charge carriers.

* Liquid State Still Restrictive: While the structure becomes less rigid in the liquid state, the ionic bonds remain strong enough to restrict the movement of ions.

* Limited Charge Carriers: Even in the molten state, there aren't many free electrons or ions readily available to carry electrical current.

However:

* Electrolysis: Aluminum oxide is crucial in the production of aluminum metal through the electrolysis process. While it's a poor conductor itself, the addition of cryolite (Na3AlF6) to the molten mix helps lower the melting point and improve conductivity, allowing for the electrolysis process to occur.

In summary: While not a good conductor in its pure liquid form, aluminum oxide plays a vital role in industrial processes due to its unique properties.