Until they are sober for a year, it is tough to determine mental health issues apart from addiction issues.
Sounds like you are ready to let go and detach with love. This is just too much to
comprehend. There is no answer to why.
I too hope your son has some influence that makes him open up to a different way to live. Often that influence does not come from the family, although sometimes it does.
May you know peace as your son struggles.