The problem is that they need an honest man in that job. Any honest man in the job usually resigns shortly thereafter because once they give him the keys to the kingdom and he knows what the accounts say, he wants to tell the people who live there that they are utterly doomed.
What he'd really like to do is climb on top of a public monument in sackcloth and ashes and scream out "ITZ COMING!" but instead he is told to offer his resignation. This is why any sucker who lands this position resigns soon afterwards.