I am pretty much a tea-totaller. I am also allergic to marijuana, so I have no desire to be around it. But I have known people in person and read articles and the like. One example that comes to mind: 16 year old boy's brother is gruesomely murdered, he becomes an addict or alcoholic and when he is 19 he decides to get clean and sober. So, he's had three years to process his grief and he is now a legal adult, not a helpless legal minor who can't do much about anything wrong in his life. Now, he wants to be sober and talks trash about what a bad person he was for using/drinking and blah blah blah.
My best guess: It is easier and/or more socially acceptable to blame drugs than to admit that life really shat on them, their parents are assholes, whatever. But, in most cases, it looks to me like they use for a reason and if that underlying reason gets better, then they will tend to stop using.
I am fond of the book "The truth about addiction and recovery" which basically takes this view.