When you select an auditor you need someone who can be impartial. When you select an auditor you want someone who will actively search for malfeasance. When you select an auditor you can want to make sure the auditor has no previous relationship with the subject of the audit.
The referee shouldn't be wearing a jersey of one of the teams!
Why would we elect a Democrat to audit government spending that is controlled by Democrats in Massachusetts? Why would we elect a Republican to audit a Republican governor's office?
The office of auditor is too important to allow it to be appointed by a governor or by a legislature. Instead the duty of selecting a person who will be free from political influence falls to the group William Brandeis called "the most important office holders."
We -- the private citizens of the Commonwealth.
We must elect an auditor who comes to office without any debt to a political party or to other politicians and who will execute the duties of the office.