Only very few chose to live on the street. For many there is no choice, they are not running away, they are simply homeless, with nowhere to live. Unable to find work, unable to afford to pay the disproportionate price of rent forced upon them.
They have been forsaken by the government; robbed of human rights. They do not wish to beg but they are hungry & cold.
Drink & drugs are not the common factor, some drink or take drugs because they enjoy, some merely to keep warm or numb their feelings of despair. Many do not drink or take drugs, just people down on their luck, lost, desperate & hurting.
Some chose to live beyond the restrictions & boundaries of the man made rules of control.