In many spots, a mowed area is virtually devoid of soil life because of compaction, the lack of OM to sustain it, ground being directly parched by the sun, one or a combo of factors. Thatch (dead grass material that's not decomposing) would be evidence of this. In any kind of spot, the amount of microbes and other soil-dwelling critters would determine the speed at which decomposition can happen. Using a mulching blade so the clippings fall back to the ground, and for chopping leaves in the fall, can help stop the process of making an unsuitable environment for microbes (and larger critters like worms.) Adding any other OM small enough to fall between the blades of grass should also help. Mow higher & more often if your schedule will allow.
