Here's why:

* Continental Crust: Mountains are formed by the collision of tectonic plates, which causes the continental crust to buckle and fold upwards. This process creates thicker layers of crust beneath the mountain ranges.

* Oceanic Crust: Oceanic crust is thinner and denser than continental crust. It is formed at mid-ocean ridges where tectonic plates diverge, and new crust is created.

So, while the ocean floor covers a much larger area than mountains, the Earth's crust is actually thicker beneath those mountain ranges.