Drifters move from place to place...once their problems catch up to them, or they've had what fun they can get out of the place they are at, they move on again. They are but simple wanderers, for whatever reasons they have to be one.
Some consider them bottem feeders, just wasting everything from everyone else. Hobo's are often considered drifters. They may be homeless, but hobo's can't get around, or rely on themselves, thus they go to homeless shelters. A drifter may not have a home, but they are self reliant. They live alone, and have to rely only on themselves.
Only when they find a reason to stay somewhere, will they no longer be a drifter.