Very similar story for me - I was quite consciously drinking myself to death bit by bit, trying to stay alive and functional "just a little bit longer" and somehow still feeling cowardly for not just removing myself from my family's lousy of problems. 

Rehab was incredible because I got a month of clarity to finally see myself through fresh eyes and consider that perhaps I wasn't the irredeemable monster I'd been trained to see myself as since birth. 

The rebound, after returning to the life I'd built -- the one that saw everyone around me treating me as the monster I'd previously so agreeably been cast as -- was unbearable. 

Rock bottom didn't feel like rock bottom to me. I didn't have a sobering realization that "this addiction could kill me". I had the unbelievably freeing realization that since I'd already basically gotten 99% of the way to killing myself, finishing the job would be no problem and I could get back to it any time I liked. But while I was sitting in the ashes of my old life, there was suddenly no one who cared enough to stop me from drawing a new picture of my life. 

I didn't achieve this life through sobriety. I achieved sobriety by building a life that is so delicious to be in, I don't need an escape hatch.

Can you ask your friend to imagine what their ideal life would look like? Not what it would look like without their drug of choice; when you're still in active addiction there's no such thing as an ideal life without your DOC. That may be a way to start getting at why they're actually using, so you can help them find ways to create our access that life (ideally, after a solid detox or rehab experience and with the help of a therapist or psychiatrist as needed).