Roots cannot elongate through these special horizons, nor can water penetrate easily. Growing plants on raised beds on these soils increases the effective root zone and improves water relations. There are many functions of soil. Some are obvious to gardeners, others are not. Soil provides a physical matrix, chemical environment, and biological setting for water, nutrient, air, and heat exchange for organisms living totally within the soil, as well as the roots and tubers of plants.
Soil regulates water distribution to runoff, infiltration, or storage.
This affects movement of soluble materials including pesticides and nitrate nitrogen. Another function soil performs is the regulation of biological activity and molecular shifts between solid, liquid, and gaseous phases. This affects the cycling of nutrients in the soil and plant growth. Physical functions of soil include serving as a filter to protect environmental quality, and as support for buildings. If there's a simple answer, it must mean there is much more to the story.