Another couldn't deal with her marriage falling apart. Prison also didn't help her learn how to better deal with life.
I believe the third was turned into an alcoholic by methadone. The etiology of this one's addictions is fascinating, but I think the main consideration is the lack of stability growing up. Money was never a problem, but her family life during childhood and teenage years was ... sub-optimal.
Emotionally-stable people tend to not become addicted to alcohol, heroin, cocaine, etc. I've met former cocaine users whose attitude is "been there, done that, no need to use again." That's kind of my attitude about alcohol - I don't care for it at all, no matter the price.
A wise woman once said, "... When a person feels safe, the false ego goes away." Helping people feel safe should be the #1 priority of every effort to help someone with substance abuse problems.