Here's why:

* Density: Oceanic plates are denser than continental plates due to their composition (primarily basalt).

* Convergence: As the plates collide, the denser oceanic plate is forced to bend and slide underneath the less dense continental plate.

* Subduction Zone: This area where the oceanic plate descends beneath the continental plate is called a subduction zone.

Here are some consequences of this process:

* Volcanoes: As the oceanic plate sinks deeper, it melts, creating magma that rises to the surface and forms volcanic arcs on the continental side of the subduction zone.

* Earthquakes: The friction between the plates, especially at the point of subduction, creates stress that can cause earthquakes.

* Trench Formation: The downward bending of the oceanic plate creates a deep depression in the ocean floor called a trench.

* Mountain Building: The upwelling magma from the subduction zone can contribute to the formation of mountain ranges on the continental plate.

In short, the oceanic plate subducts because it's denser, and this process leads to the formation of various geological features like volcanoes, earthquakes, trenches, and mountains.