I'm not sure that it's an acceptance issue, but that may be a factor. The bottom line is probably related to economics. Many of the Addiction treatment facilities are private and do not take insurance, meaning the consumer has to pay up front and there is typically no refund and no guaranty that the treatment is going to be effective, whatever the standard by which treatment is considered "effective". The ones that do take insurance are typically limited to 2-4 weeks (28 days) and the expectation is that the consumer will have a discharge plan that includes outpatient or IOP or AA meetings or some combination thereof. Research typically shows no difference in effectiveness between residential and IOP programs after one years.
Mental health is seen differently and at one time there was a vast infrastructure of state run mental hospitals were consumers/patients could stay indefinitely at public expense. This was seen as "warehousing" people and not allowing them to participate in the community was seen as inhumane and arguably a violation of human rights. So called, "deinstitutionalization" started in the late 50's-early 60's when states started to close or reduce the size of their hospitals and hospitalization was seen as a last resort and only suitable for emergencies for 72 hours, more or less. Non profit agencies often do run residential MH programs, but they are hard to get into and there are usually lengthy wait times for space. There are several closed state hospitals in New England, where I grew up and the scale is impressive. One that I'm familiar with, outside of Boston, was obviously built for long term residency as it had a church, vocational training centers, gardens and orchards on site, all for the clients.
Ultimately if there is sufficient demand for such services and the will and ability to pay to make the services available, I'm pretty confident that someone will figure out how to make it available.