Here's why:

* When two continental plates converge, they do form a subduction zone. However, this is not always the case.

* Continental-continental convergence is often characterized by intense mountain building. This is because both plates are relatively buoyant and resistant to being pulled down into the mantle.

* Instead of one plate subducting under the other, they collide and crumple, causing mountains, faulting, and earthquakes.

Examples of this type of collision:

* The Himalayan Mountains formed from the collision of the Indian and Eurasian plates.

* The Appalachian Mountains were formed from the collision of North America and Africa.

In summary:

While a subduction zone can form when two continental plates converge, it's not always the case. The most common outcome is a collision zone, where mountains are built.