It works for most people. Works for me, my friends, and with any business functions I attend. Unlike yourself who is not deterred, I can't say I know anyone who shrugs off the cost or stigma of a drunk driving offense. It's a big black mark on ones character, insurance, etc.
The 'deterrent' is very much there but, as Chuck states, folks who are habitual offenders have other issues such as alcoholism, drug addictions and so on.