Cleaning up the leaves in a suburban lawn is rarely enforced or legislated. It is just an expected task for the suburban homeowner: thou shall not have many (or any) leaves in your lawn by the end of the fall season. Why is this the case? Here are a few possible reasons:

1. A well-kept lawn, from green grass neatly kept to an absence of weeds to being cleared of leaves, is a marker of social class. It is part of keeping up the neighborhood and supporting property values. Lack of attention paid to the lawn signals less-invested homeowners, less valuable properties.
2. Clearing leaves is an unquestioned social norm that simply continues on because people did it before. That leaves could be beneficial for lawns and garden beds may not matter; the inertia is already there for clearing leaves and it could take time for new patterns to emerge.
3. There are commercial and industrial forces invested in making sure lawns are seeded, treated, and cleared. There are rakes and leaf blowers to sell. It is big business helping Americans remove leaves.
4. Suburbanites pass along this social norm to each other through conversation and exhibited behavior. Neighbors share words while outside about their lawns. One suburbanite rakes their leaves because they see their neighbors doing it.

Perhaps this practice will pass into history at some point. But, as long as we have a suburban emphasis on single-family homes and their lawns, there will be more years of raking, bagging, mulching, and clearing leaves.