Trees and shrubs don't usually get proper nutrition in a manicured type environment. Grass roots will absorb most all nutrients before deeper tree feeder roots get a chance.
Trees and plants in nature get nutrients from decomposing plant matter like leaves, wood, etc. that break down to rejuvenate the soil. In a well maintained property these materials are constantly cleaned away which over time allows the soil to lose its ability to properly support trees and shrubs. Read more