Why do Americans shit where they eat?

What benefit is there to consistently dousing your lawn with chemicals for the soul purpose of aesthetics?

related: two of my neighbors across the street just had their lawns sprayed for weeds. Guy in huge truck pulls up with a huge tank and just starts spraying the lawn. I could smell it all the way into my yard.

Is there any specific scientific research to show how harmful weed control is to both the environment and human health?