Housing is pretty much a prerequisite for fixing the other problems. I would guess that's it's almost impossible to kick something like a drug problem while sleeping on the streets.
The gist of the interview was, don't judge the homeless for drugs and alcohol. It's often the only comfort they have. What would really help is a home, but the cost of housing is so high that saving all of your booze money would never be enough to rent an apartment anyway. Might as well spend it on something that will make you feel a little better.