[treis]

The mentally ill were confined to institutions.

The more functioning homeless put enough scratch together to get a place at a flophouse.

I think it's also policing. There was a time that a bum who got caught in the wrong place got the crap kicked out of them by the cops. Obviously problematic for so many reasons but violence does have its way of modifying behavior.

Also drugs. Just way easier to get and more powerful than before. Back then it was mostly alcohol. While that takes a terrible toll on one's body most alcoholics are functional to a reasonable extent. Not so much for crack or heroin or meth addicts.