Minecraft wiki entry for Hunger_management, associated text: Disadvantages:
Beetroot seeds can be hard to find; they can be obtained from village farms, structure chests (snowy village, mineshaft, dungeon, end city, woodland mansion), and wandering traders.
Beetroot grows somewhat slower[verify] than other crops, and they only yield one beetroot for each plant.
Individual beets have minimal food value, with only 1.2 saturation a piece.