Recovery doesn't happen all at once. Sometimes dealing with one problem at a time is better.

Addressing the mental health issues that lead to addiction can be incredibly difficult while also dealing with the issues brought on by the addiction itself. Maintaining sobriety while working on yourself is difficult, but for many it's easier t9 start there than to correct their thinking while fighting off withdrawal.

The reason rehab can work is that, ideally, it lets you get clean in an environment that's easy on your mental health, and begin to work on your mental health in an environment where it's easier to maintain your sobriety. Holistic doesn't mean simultaneous.