If the addict can't find drugs anymore, he can't use them.
If the alcoholic can't find alcohol anymore, he can't drink it.
If the gambler can't find slot machines, he can't gamble.
If the overeater can't find food, he can't eat.
The same can't be said for depressed and unmotivated people - there's nothing you can take away from them in order to keep them from suffering depression or demotivation.
Since they themselves can't take those things away from themselves for their own good, the addic, the alcoholic, the gambler and the overeater really suffer from the same problem, lack of self-control.
EDIT: atwebb:
Since having self-control would suffice to stop using drugs, drinking alcohol, gambling, and overeating, therefore one who can't stop doing any of those has to be lacking self-control.
Tell me where you got lost in that argument.