Because people are smart enough to separate what he's done professionally from what he has done privately. Crack smoking aside he has fulfilled the duties of his office exceptionally and saved the city a disgusting amount of money.
Frankly if I were any previous mayor I'd be fucking ashamed that a crack head performed my functions orders of magnitude better than I did sober.
He campaigned on cleaning up city hall, cutting rampant fraud, overspending and fiscal irresponsibility and actually delivered which never happens in politics.
You should double check the amounts of money he says he's saved the city. Not as massive as he'd have you believe.
Still. Better than spending the savings on crack, eh.... oh wait....