I honestly, genuinely, fail to understand the meaning of that. It can't possibly be true that homeless people didn't exist before the 1980s. What does this actually mean?
Second, more crazies were institutionalized. Santa Clara County used to have "The Great Asylum for the Insane.", opened in 1885. This was a huge complex of buildings in a rural setting. The place was later renamed to Agnews State Mental Hospital, later Agnews Developmental Center.[2] Beginning in 1972 this was gradually shut down. The last patient was kicked out in 1998. The remaining buildings are now owned by Oracle, and you can go look at some of them if you want.
Third, vagrancy used to be be illegal. Cops arrested people for it, and they were sorted out into "too lazy to work", "unable to work", or "crazy". This peaked during the Great Depression, when the Works Progress Administration was created to give unemployed people jobs.[3] At peak, the Federal government employed 3 million people, mostly doing construction work. There was some really nice construction. Rincon Annex, the old post office in San Francisco, is one of the finer local examples.
As the demand for unskilled labor declined, finding some place to send the "too lazy to work" people became difficult.
Fourth, drugs. There are too many burned-out people who aren't coming back.
[1] https://en.wikipedia.org/wiki/Robert_Taylor_Homes
[2] https://en.wikipedia.org/wiki/Agnews_Developmental_Center
[3] https://en.wikipedia.org/wiki/Works_Progress_Administration
The modern world is terrifying and confusing, but every so often some small nugget of information comes along that makes profound sense.
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.
https://www.thoughtco.com/hoovervilles-homeless-camps-of-the...
Kids growing up on the streets used to be extremely common.