What would you do if you found a piece of trash in your room?
What would you do if on the floor of your room, there was a poorly disposed wrapper or paper, alerting you to its presence by its jarring contrast to the relatively tidy room? You would probably pick it up and dispose of it properly. Or perhaps, if you were feeling particularly lethargic, you would at least make a mental note to clean it up later. These are both natural responses to a minor disturbance within a personal space; things that we do without even thinking about it much.
We feel a sense of responsibility for the spaces that we occupy. So, when our space is dirty, we respond by cleaning it up. In contrast, you may not be particularly interested in going out of your way to clean up and maintain a random space outside your home. For example, if you saw the same piece of trash on the street, your immediate response might not involve taking the responsibility to pick it up and throw it away properly.