I was literally saying most of this to my wife just now.
We're right on the edge of suburbia, I can see grazing cattle from my backyard. Here in South Australia there are 2 people per square kilometre.
One other factor I think is worth mentioning, is young people living in vans, while working and socialising over the internet.
Digital nomads finding an empty house; discreetly parking the van in the driveway for a week, while they check the place thoroughly for provisions, vegetable gardens, weapons, valuables and private keys; then moving on when the place is picked clean.
Spend a day in the backyard, watching the surrounding houses for signs of life, to find the next squat
These people aren't paying mortgages, they're almost impossible to find unless they want to be, and if they're organised, they can plan to revisit each place as any fruit trees or veggie patches ripen. Life finds a way :)