To jump off of your post; Whether it is H or opiates, or any other
addiction, it is my firm belief that it is b/c of genetics, or their brains are wired differently. I've lived with someone addicted to alcohol, many years ago. Promises to quit were never kept, found stashes hidden around the house. Made it one time for 2-3 days til the DTs hit. That was a pretty unsettling event to put it mildly. I finally told them that they had to move on, I couldn't take it any longer.
The addicts that I've been around were not in a clinical setting. These were my friends, they have eaten at my table and slept under my roof. I'd known them for many years. Many are gone now. Some tried AA, some tried NA, some had families with the finances to get them into private rehab, some were able to succeed with methadone, for quite a few nothing helped, and not so long ago I've watched parents bury their child who swam in the same rivers and creeks with mine.
The SAP certificate that they get, if they get tossed in jail for awhile isn't worth the paper it's written on. It does not prepare them for going back into the community from whence they came, especially if it is a very small one where all of their friends, and family, live and some are also using what got the newly released person busted.
The idea that an addict can walk up to a treatment center and just check themselves in is a fallacy. I guess if you have thousands of dollars at your disposal for a private one you can do so but most folks w/a drug problem don't. Took three months of calling, every single day, just to keep their name on a list for a bed opening (I know, b/c I did the calling, as the facility didn't accept calls from inmates), to get a loved one into one. If you missed a day of calling your name was removed and you had to start over at the bottom of the list. That was tough for me to remember. I had to set a reminder on my phone. I was calling three places, who agreed to put the person on the list, every day. The places only took folks referred from court. I called almost every facility in this state (no point in calling the ones for only the opposite sex).
https://www.drugabuse.gov/publications/drugfacts/genetics-epigenetics-addiction