One reason is that San Francisco is the cleanest city in the world. Every business must collect their own garbage and dispose of it properly. This policy makes it hard for businesses to fail because they have to get rid of their garbage. Another reason San Francisco is so clean is its strict enforcement of zoning laws. These laws make it difficult for businesses to build without following specific guidelines. This limits the amount of trash that can be generated and makes it easier for the city to clean up after itself.