Here's why:

* Carbon's Bonding Ability: Carbon has the unique ability to form four covalent bonds with other atoms, including other carbon atoms. This allows for the creation of long chains, branched structures, and complex rings.

* Versatility: Carbon can bond with a wide variety of other elements, including hydrogen, oxygen, nitrogen, and sulfur. This diversity in bonding partners leads to an incredible variety of organic molecules with distinct properties.

* Foundation of Life: Organic molecules are the building blocks of life. From carbohydrates and lipids to proteins and nucleic acids, all essential biomolecules contain carbon as their backbone.

While other elements can be present in organic molecules, the presence of carbon is what defines them as organic.