That’s sort of how addiction works. Drugs are a lot of fun and feel good for a long time and that lets you ignore negative consequences way past the point that someone not on drugs would make a change in their life.
People who are addicted to heroin would rather do heroin in a muddy ditch than be sober in a 5 star hotel.
The psychological problems that lead to addiction of any kind are very deep. The addiction itself is just a symptom.
What this decision is - is just a declaration of "let's stop fighting symptoms, maybe that will allow us to see the root problem".
You are correct that most of them had hard lives to begin with. Happy people with strong support networks don’t tend to use heroin, I wouldn’t think.