Considering that DUI has a high recidivism rate, saying they are not likely to re-offend is absurd. You seem to be arging that the penalty for a DUI should be the same regardless of whether no damage occurred or the drunk kills a family of four.
DUI might, but does vehicular manslaughter during a DUI?
And what is giving you the impression highlighted in your second sentence?
Because a person who drives to someplace else and then drinks can be presumed to have made while sober the premeditated decision to drive after drinking. The same is unlikely to be the case for a person who drinks at home. The inability to show premeditation for the act of driving after drinking that caused the death is why a lesser penalty would be appropriate in such cases.
I suppose that's true, but I doubt many people set out thinking, "hey, I'm going to drive drunk tonight." Not that I have much sympathy for those who do.