The lawn has grown in popularity in landscape architecture beginning about 300–400 years ago. It’s considered aesthetically pleasing to many to have an expanse of green around one’s home. Grass can be a vivid shade of green, it’s fairly easy to grow, and it makes a pretty ground-covering. However, as you mentioned, people get out of hand with the lawn maintenance thing. Part of that is because people worry about maintaining the house value, another part is that people have their hobbies and obsessions. Lawn care seems to be one of these things. Lastly, it is kind of fun and satisfying to grow and tend plants. :)