Here's why:

* Formation: Igneous rocks are formed from the cooling and solidification of magma (molten rock) or lava.

* Vast Sources: Magma and lava exist deep within the Earth's crust and mantle, providing a constant source for igneous rock formation.

* Oceanic Crust: The majority of Earth's crust, the oceanic crust, is composed of igneous rocks like basalt and gabbro.

* Continental Crust: While continental crust is more varied, igneous rocks like granite are still abundant.

While sedimentary and metamorphic rocks are also important, they are derived from existing rocks, including igneous rocks.