Why does the quantity of salt demanded tend to be unresponsive to changes in its price?

It is because the demand for salt is inelastic.

Explanation.

Inelastic Demand refers to the concept of microeconomics which implies that the quantity demand of commodities won't be affected by the rise or drop in price. This concept can be reflected in everyday life commodities such as sugar, salt, and wheat.

For example: People won't buy sugar more than they need if price is down or they won't buy less if the price is high, they would buy the quantity they require.

Same goes with the salt prices high or down, it demand won't change.