The shown shape of the dispenser’s outer shell means that the bearings (cylindrical with flat circular faces, visualized as the grey outline of a circle above) would be fit into a curved surface. Aesthetically, this means the edges of the bearing would be shown and the unit would look poorly designed.

The purpose of the curved faces in the current design as shown above are to allow the user to put several of these units, side by side, around the base (metal pole in the middle of the white kidney lazy susan shown to the right) of an in-unit spice carousel such as this one: