Polygonal 3D models are sharp because their surfaces are made of flat, connected polygons (like triangles or quadrilaterals) that form distinct angular edges.
Unlike smooth-surface models (e.g., NURBS), polygonal models rely on these flat faces to define shape—fewer polygons mean more pronounced sharp edges, while more polygons can soften edges but still retain crispness if designed for it.
To get a smoother look, you can add more polygons or use subdivision surfaces (in tools like Blender) to smooth edges without losing the base polygonal structure.