Why do wine bottles have different shapes?

It represents the region or varietal to some degree. A Bordeaux varietal, such as Cabernet Sauvignon and Merlot, is narrow and has a defined shoulder where it quickly slopes out from the neck. The Burgundian varietal of Pinot Noir is fatter and gradually slopes from the neck to the body. There’s no definite spot where the neck begins and the body ends. These two bottle shapes evolved out of tradition from Europe. Most winemakers continue to honor their European ancestors.