Here's why:

* Granite's Composition: Granite is a coarse-grained igneous rock primarily composed of quartz, feldspar, and mica.

* Metamorphic Process: When granite is subjected to intense heat and pressure deep within the Earth's crust, its minerals recrystallize and align. This process, called metamorphism, changes the texture and sometimes the mineral composition of the original rock.

* Gneiss Formation: The alignment of minerals during metamorphism creates a distinct banding or layering in gneiss. The original minerals from granite are still present, but their arrangement is altered, leading to the formation of gneiss.

While other metamorphic rocks can form from granite, like schist or migmatite, gneiss is the most common due to the widespread presence of granite and the typical metamorphic conditions that lead to its formation.