A uniform, well kept lawn serves a specific purpose. It demonstrates the conformity of the resident citizen.

A good well behaved citizenry keeps their lawns neat and uniform. A misbehaving citizen allows his lawn to fall out of uniform. A wildly deviant citizen, one who may be "a danger to the social order", allows his lawn to fall entirely out of the norm. (Perhaps by planting a garden, or allowing a natural meadow to grow there.)

The "problem" of the social deviant is solved by using legal measures to either force him to conform or to eventually evict him from the neighborhood. What the government does not want is people falling out of line with the officially designated social norms. Manicured lawns is one way they can effectively measure compliance, and it is a warning sign of a potential deviant. It is one way they monitor and control society.