I lived in an apartment where 6 out of 8 apartments were occupied by alcoholics or drug addicts.
Nearly every block on that street was the same. This was Glasgow, and the drug of choice was heroin, although everyone also smoked as much marijuana as they could afford. These people's lives weren't particularly shit on a day-by-day basis, but they had nothing but misery on the horizon. If they had kids they would lose them, they would never work, never be praised. They'd never see the world. Most of them hadn't been outside Glasgow for years, if not the whole of their lives. They would probably never go to the beach or on even the shittest package holiday. Those who were obviously junkies (struggling to walk, sunken faces and destroyed skin) were basically seen as an underclass by everyone from their peers, to the rest of the population and the police.
But there were people living in the same street, in the same apartments, with far less money, working shitty jobs, who weren't even open to taking drugs. The structure of this area wasn't bad at all - it could have been Rat Park, if it wasn't filled with drug-addicted rats who just pissed in the common areas and threw their rotting food out of the window.
I don't have any great insight here - but I think there's more to it than environment as suggested by this study. There are people all around the world who live in far worse conditions and who aren't turning to substances, even when they are available.
My feeling is that rats living in cages, who can see rats living in Rat Park would be more likely to seek addiction. And perhaps even more so if they see other rats being moved from cages to Rat Park, but not them. I don't know if rats could understand this concept though, which might be why they aren't all living in Afghanistan's poppy fields.