Here's why:

* Submarine Volcanism: Mid-ocean ridges are underwater mountain ranges where tectonic plates diverge. As the plates move apart, magma rises from the mantle and erupts, forming new oceanic crust. This process, called seafloor spreading, is responsible for the vast majority of volcanic activity on Earth.

* Massive Scale: The mid-ocean ridge system is the longest mountain range on Earth, stretching over 40,000 miles. The volume of volcanic material produced here is immense and ongoing.

* Other Volcanic Sources: While mid-ocean ridges are the dominant source, other volcanic areas like hotspots (e.g., Hawaii) and subduction zones (e.g., the Andes Mountains) also contribute to volcanic material production, but on a smaller scale compared to the mid-ocean ridges.