How do you know? Do you ask everyone you meet for an ID?
There's a lot of people who live in the "fringes" of society who don't have an ID.
My uncle, for example. He lived with my grandma his whole life and didn't have a driver's license, car, or a job other than to run errands for my grandma.
I also have a friend who does not have an ID. Her husband takes care of everything and she doesn't drive.
It's unusual but not illegal to live like that.