>In the US, the homeless population exploded, in the 1980s, when they closed down all the mental institutions

it was the 1970s, SCOTUS decision in O'Connor v. Donaldson, when the court said that the mentally ill who were not dangerous could not be held in institutions against their will. The 1960s had seen a series of scandals concerning callous treatment of inmates in institutions (for example, see Titticut Follies) and that created the climate for deinstitutionalization.