I think the highest nutrient densities of soil happen when organics are varied and recycled. Lawn grasses are usually mowed, and often the cut grass is removed rather than allowed to replenish the soil. Also, if the grass is treated with pesticides, that means no soil microbes. Also ornamentals are pruned and hauled away, instead of being recycled to the soil. i know trying to grow vegetables on soil that formerly had lawn, requires a lot of replenishment.
