Here's why:

* Salt's Mechanism: Salt melts ice because it lowers the freezing point of water. This means that the water will remain liquid at a lower temperature than it would normally. The salt dissolves in the water, creating a salt solution with a lower freezing point.

* Spices' Properties: Most spices are organic compounds that don't have the same chemical properties as salt. They don't readily dissolve in water and don't significantly alter the freezing point.

While some spices might have a slight effect on ice due to their chemical composition, it's not a practical or significant effect compared to salt.