[Viliam1234]

You perceive the sidewalk in front of your house as something that is related to you, and you know people in your culture would judge you if the sidewalk is dirty. But this is a cultural concept. You could also have a cultural concept that only things inside your house reflect on you, and the sidewalk is... just a random part of universe. Then there is no reason why you should go and clean up a random part of universe.

You probably don't feel that it is your duty to go and clean up garbage everywhere in your city. At some distance, it's simply not your problem anymore. This is the same, but the distance ends at the threshold of your house.

Any norm makes sense, internally, if you know that this is the norm others will use to judge you. Most people don't go beyond what is required of them.