The world of football is, by and large, an art rather than a science. Sure, recent years have brought a hefty amount of analytics into the sport, but more often than not, they are not the centerpiece of a football operation. The NFL Draft, free agency, and coaching hires can often be a roll of the dice. Even if a coach might seem like an awful hire at the time, he might pan out. The opposite is true, and you can look up “Hue Jackson Cleveland Browns” if you want an example.
The point is, coaching hires can be pretty risky business.