Prior to hiring Bohn, CU had never hired anybody from outside the CU family. Going all the way back to Henry Carlson, it had always been a former CU coach or high level assistant AD (in the case of Tharp). Those guys were fine, but lacked the vision to take CU to the next level. Marolt wasn't responsible for hiring Bill McCartney, and he didn't want to be bothered finding a replacement for him, either.
You're trying to tie the success of the athletic director to the success of the football team. That's easy to do, but misguided. Marolt was a good-old-boy and he didn't screw up. I'll give him credit for bringing back three sports after the debacle in 1980. What was handed to him, football wise, was a gold mine. He did nothing with it.