They are sweeter tasting. It is a major cooked vegetable in many Near Eastern cultures. The older types are usually called mangel or wurzel. Swiss chard is a cultivar of the petioles of the leaves. Sugar beets are forms that have been selected for higher sugar concentration.
Red beets are comparatively recent.
Beets and chard have been eaten for thousands of years in the Near East and the Mediterranean area. The ancient Greeks mentioned these plants in their writings. Spinach is sometimes substituted for lettuce in salads. Native to western Asia. Domesticated after the time of the Roman Empire.