Why can't Rhubarb be harvested the 1st and 2nd years?

Rhubarb can't be harvested the 1st and 2nd years because Rhubarb needs that time to establish its root systems.

If you were to harvest it, the plant would then spend its energy making more stalks and leaves and not on root growth.

Although during the second year, you can harvest some stalks, but only a 1/3 of the plant.