Because addiction does not follow rules and takes no prisoners. The drug of choice becomes the abuser's whole world- regardless of money, family, marriage, career, morals, ethics, reputation. Eventually perhaps even life.
There is no 'why', for me there just 'is'. To break free of the hell I created required the most significant of reminders life has to offer. To break the cycle of addiction meant I had to become as driven in healing and not (in my case) drinking- ever again. Every relapse is worse.
Empathy and support offered. Addiction sucks- death is worse.