They didn't want someone that they could manipulate. They reacted to the supporters disquiet with Duff and decided to appease them by appointing someone close to Martin, who for bizarre reasons was still held in high regard by a vocal minority.
In reality they should have gone for someone somewhere between the two instead of appointing Russy 2.0, which unfortunately at the moment they appear to have done.
Still time for him to turn it around, but so far he's stuck close to his mentors playbook. Tedious, possession obsessed football, playing people out of position, firing blame in all directions but at himself. He needs to buck himself up.