Well, you can't really blame the fighters. They hire coaches for a reason. If they go against what the coaches tell them then it's on them. But on the other side of that, it's not uncommon for the fighter to walk all over the coach and do what he wants to do. At that point they just become "yes" men. In the long run it damages the fighter and the coaches reputation.
It is the fighter that hires a coach, only they themselves in the end can truly assess what they can or cannot do. A coach is simply there to assist them in reaching their potential, providing needed structure and to develop themselves further. There is indeed a fine line, as you yourself must know, between a good coach, a bad one, and a friend who just so happens to coach you.
Considering it is the fighter in the end who is in the cage, whose livelihood depends on success and prolonglivety in the sport, it is their end-responsibility to ensure they are healthy come-fightday. Those who in professional sports still haven't figured out the business-side of their branch, should have remained in their local bareknuckle fighting-ring.