Why was this shape not used for Coke bottles?

The Coca-Cola bottle, called the "contour bottle" within the company, was created by bottle designer Earl R. Dean. In 1915, the Coca-Cola Company launched a competition among its bottle suppliers to create a new bottle for their beverage that would distinguish it from other beverage bottles, "a bottle which a person could recognize even if they felt it in the dark, and so shaped that, even if broken, a person could tell at a glance what it was."

This prototype never made it to production since its middle diameter was larger than its base, making it unstable on conveyor belts.