Why is flat seam also called dressmakers seam?

The flat seam, often referred to as the dressmaker's seam, is a technique primarily used in garment construction to create a clean, smooth finish on the inside of garments. This seam is particularly favored by dressmakers because it reduces bulk and allows for a more polished appearance, making it ideal for lightweight fabrics and fitted garments. Its design helps garments lay flat against the body, enhancing comfort and aesthetic appeal.