Because they benefit so enormously from the agglomeration effects of being adjacent to it. That density is the only reason they exist in the first place. If my

Because they benefit so enormously from the agglomeration effects of being adjacent to it. That density is the only reason they exist in the first place. If my wife declared the kitchen to be a separate part of our apartment that she's not responsible for but then came into the kitchen every single day -- worked there, ate there, met friends there -- without ever participating in the maintenance of the kitchen, then I would think she's shirking her responsibility to the whole (and I'd be right). "What's the problem? I have defined the area where I sleep to be independent of the kitchen! What part of that don't you get?" is not a compelling argument.