The contrast of good times and a burgeoning population of homeless people doesn't jibe. How is it that with the economy chugging along nicely the homeless population is increasing? Many assume some of the homeless choose their existence. But people who work with them scoff at the assumption. They cite poverty, a housing shortage and untreated mental illness as the real reasons people become homeless. A small Minneapolis program called Spectrum helps the most vulnerable homeless people - the mentally ill who live outside in the winter.