Why so many homeless? According to the National Coalition For The Homeless there are two trends largely responsible for the rise in homelessness: a growing shortage of affordable rental housing and a simultaneous increase in poverty.
Homelessness and poverty are inextricably linked. Poor people are frequently unable to pay for housing, food, childcare, health care, and education. Difficult choices must be made when limited resources cover only some of these necessities. Often it is housing, which absorbs a high proportion of income that must be dropped. If you are poor, you are essentially an illness, or an accident away from living on the streets.
Another reason why homelessness persists is because of falling incomes and less secure jobs which offer fewer benefits. Low-wage workers have been left behind as the disparity between rich and poor has mushroomed. To compound the problem, the real value of the minimum wage in 2004 was 26% less than in 1979. This means the guy who serves up your burger or the lady who cleans your motel room when you are on vacation is living on the edge.
Declining wages, in turn, have put housing out of reach for many workers: in every state more than the minimum wage is required to afford a one- or two-bedroom apartment. Unfortunately, for many millions of Rhode Islanders more then 50% of their salaries go towards renting or housing costs, resulting in sacrifices in other essential areas like health care and savings.
A good read called "Hand To Mouth" by Linda Tirado brings it all into focus. You can listen to her tell it like it is here