The problem for the police is that there would be an outcry if they just battered down the doors of people's flats because no one had seen them for a while. A few days on Mumsnet will tell you that a lot of people just won't open their doors. So you can imagine them knocking and calling out and not hearing sounds of distress from within and leaving. Quite a lot of people go away for months or years, specially those who have family they might visit in another country. They wouldn't be happy to come home to find the police had broken in to their home because they weren't around.
Likewise Peabody can't just barge in to people's homes, again just read Mumsnet to see how much people object to their landlords wanting entry.
What I take from this is the importance of maintaining social contact, even on a minimal level, with those around us.