Here's why:

* Abundance: Cellulose is the most abundant organic compound on Earth. It's the primary component of plant cell walls, making up a significant portion of wood, cotton, and other plant materials.

* Structural Role: Cellulose forms long, unbranched chains of glucose molecules that link together via strong hydrogen bonds, creating a rigid and strong structure that provides support and protection for plant cells.

While other polysaccharides like chitin (found in exoskeletons of insects and crustaceans) and peptidoglycan (found in bacterial cell walls) also have structural roles, cellulose is far more prevalent in the overall biomass of living things.