Here's why:

* Solubility: Limestone is composed primarily of calcium carbonate (CaCO3), which is readily soluble in slightly acidic water. This solubility is the key factor in karst formation.

* Formation: Limestone is often formed from the accumulation of marine organisms' shells and skeletons over millions of years. This creates large deposits of the rock.

* Karst Features: The dissolving action of acidic water on limestone creates the distinctive features of karst landscapes, including sinkholes, caves, underground streams, and springs.

While limestone is the most common, other rocks can also form karst landscapes, though they are less frequent:

* Dolomite: Similar to limestone, but contains magnesium carbonate.

* Gypsum: A sulfate mineral that is readily soluble in water.

* Rock Salt: Although uncommon, salt can dissolve in water and create karst features in arid regions.

So, while other rocks can contribute to karst, limestone is the dominant and defining rock type associated with karst landscapes.