Here's why:

* Hardness: Diamonds are the hardest naturally occurring material on Earth. They are only scratched by other diamonds due to their strong carbon-carbon bonds.

* Cleavage: While diamonds are extremely hard, they do have perfect cleavage along certain planes. This means that a sharp blow from another diamond can cause the diamond to split along those planes, creating a cut.

While other materials like tungsten carbide can be used for industrial diamond cutting, they don't truly "cut" the diamond like another diamond does. They create friction and abrasion that wears the diamond down.