Here's why:

* Formation: Breccia forms from the accumulation and cementation of angular rock fragments (clasts) that are larger than 2 millimeters in diameter. This process occurs due to geological events like landslides, volcanic eruptions, or tectonic activity.

* Angular Clasts: The defining characteristic of breccia is its angular clasts. These fragments haven't been transported very far or haven't been exposed to significant weathering, which would have rounded them.

* Cementation: The angular fragments in breccia are held together by a cementing material, which is usually a mineral like calcite or silica.

While some breccia may undergo metamorphism later in their geological history, their original formation process classifies them as sedimentary rocks.