Here's why:

* Mid-ocean ridges: Basalt is formed from the cooling and solidification of magma that erupts at mid-ocean ridges. These ridges are where new oceanic crust is created.

* Volcanic activity: Basalt is the primary rock type associated with volcanic activity on the ocean floor.

* Composition: Basalt is a mafic rock, meaning it is rich in magnesium and iron. This composition is typical of the magma produced in the Earth's mantle.

While there are other igneous rocks found on the ocean floor, basalt is by far the most abundant.