From a partner who used to work in one, people:
- didn't trust the program and wouldn't sign up
- didn't actually want to quit using so they avoided it
- wanted to get the benefits from the program without changing anything (i.e. showed up to get free food etc)
- tried but didn't like it and went back to using
Very few people actually went all the way through compared to the population in the city that could have used it.
The real question is: how do you help people who do not want your help. Do you let them waste away and die on the sidewalk, or do you institutionalize them?