Young bored person tries some meth at a party because they're bored, young and invincible. They like it and do it again, a few times, and now they're hooked. They want more all the time. Due to constantly being high or looking to get high, they fail at work or flunk out of school. What happens next?

If that person is from a wealthy family, maybe their family pays to put them into rehab, or brings them back to live at home, or pays their rent. The wealthy family has the resources to support the addict in some way and usually manages to keep them off the street.

If that person is from a more common sort of working class family? They have less money available to them, so they'll start to steal. They'll steal from their family, who don't have much in the first place. They'll get in fights about it and alienate themselves from their family. The house is small so everybody in it has to live close to everybody else, the situation becomes intolerable and eventually the addict is kicked out and cut loose. The family can't afford to do otherwise. They tell the addict to get clean and wish them luck. He's now homeless and will probably be dead in a few years.

Most street users aren't using because they're on the street. They're on the street because they're using.