They have all been around for what seems like forever and are all technically homeless. The homeless problem in America is not new.
In the age of political correctness, even the panhandler on the street corner may get offended if you call him a bum when he considers himself a hobo or a tramp. There are definite differences in the meanings of these words.
A hobo as an example is a homeless person who travels from town to town, looking for odd jobs. Sometimes they are migratory laborers traveling between jobs before working yet again. A hobo then, who works on-and-off may take offense when called a bum because most bums never work and rarely travel. I'm reminded of the bad old days when hobos would knock on back kitchen doors offering to do a few chores for a meal and a cup of coffee. It was an accepted way of living back then when jobs were in short supply.
The homeless hobo seemed to get his start right after the US Civil War when so many were discharged to look for employment when there wasn't any to be had. “Hobo” then came to be defined as “an idle, shiftless wandering workman, ranking scarcely above the tramp.”
The word “tramp” comes from a Middle English verb meaning to “walk with heavy footsteps.” Like “hobo,” it also started to be used after the Civil War. Ultimately "tramp" came to be used to define those who “prefer the transient way of life.” While the term “tramp” isn't used much anymore, it has never completely left our use in the English language.
Whatever you call the homeless, you can be sure that they have been around in great numbers for a very long time and haven't really changed that much.
Maybe it's us and our attitudes that have changed.