And why are you assuming that these people are not getting any other help? The two aren't mutually exclusive. In fact, not having to deal with all of the risks and stresses of scoring illicit drugs probably makes it significantly easier to make improvements in other areas of your life (which, as well as being a good thing in itself, might in turn make it easier for you to kick the addiction).
Absent convincing evidence to the contrary, it's entirely plausible that this approach is doing a good job of getting people off heroin, as well as improving the lives of those who stay on it. The fact that some people remain addicted doesn't undermine that.