People who choose to live on the streets. Go talk to people. Ask where they're from. The people you're most likely to encounter (the ones being visible, doing drugs visibly, camping visibly) are travelers of sorts. Adventurers even. Sure, many are drug addicts or have mental health issues. But so do millions of people with jobs and homes. Unlike those people, these people choose to eschew social norms wholesale and live a nomadic lifestyle.
You see much less of this outside of the temperate climate of the West Coast. But here, it's a growing problem. They have plenty of food and can earn above minimum wage by spare-changing and are given adequate healthcare. And they shit and piss on our streets, block sidewalks, litter profusely and otherwise do whatever they feel like.