I think the pest and disease problems lawns may have are created by trying to get more out of the grass than it has to give us. Lawns are watered too much, over fertilized, mowed too closely, and have chemicals applied to the point of killing off all the beneficial and affiliated microbiology that acts in partner to keep the environment in ‘balance’, preventing infestations. Automation of watering and the desire to get value from one’s sprinkler system leave the plant and soil constantly wet which creates a healthier space for fungus than grass. Lawns aggressively fertilized push too much growth on the grass plants making for soft, tender foliage that is susceptible to infestations because of the lush nutrient density it creates - its like sugar candy to tiny insects.
Grubs are probably the most likely problem of a lawn at the opposite end of the managed spectrum. Light and balanced fertilization will reduce a lawns susceptibility to grubs but grubs are not the result of poor management - in my opinion. However, more often than not, if I come across Japanese Beetle Grubs, I take a quick scan around me and more often than not, you will find ornamental plants and trees that the adult Japanese Beetles like to feed on. Take a look around and you will find Little Leaf Lindens, Purple Leaf Sandcherry, and Roses, among others.
Grass does need a pound or two a year of nitrogen from fertilizer every season but Generally speaking, the fewer inputs into a lawn, the fewer problems.