You actually answer your own question:
Question: I can’t help but wonder, why did life turn around for them but it hasn’t for my addict ex yet?
Answer: every addict is different
I don't think that's what is at play here really. You know enough about addiction to know that people stop (or not) when THEY get to it and not one minute before.
So unless I am misunderstanding you, I'm not sure why this is even worth wondering about?
So let me ask you, when you ask yourself that question - why hasn't he yet - what is your theory?