I process health insurance claims for a living.

So, as far as rehabs go, there are different kinds. There are acute psychiatric facilities, which usually only assist the patient through immediate withdrawals. After that, these facilities with either refer you to a substance use disorder rehabilitation facility (SUDRF) or a residential treatment center (RTC) if you're under 21. (Note that RTCs treat both mental illness and substance abuse disorder in individuals under 21 years of age).

All three of these types of facilities are eligible to be paid by health insurance. The rehabs you see on TV are undoubtedly one of these.

However, there is another type of rehab that is not eligible to be paid by insurance, and that is religious rehab. [See programs relating to Adult and Teen Challenge].

Because of their unorthodox and unproven methods of rehabilitation, insurance will not cover treatment, and therefore renders the patient responsible for the cost of "treatment".