Coordinating Big 12 defenses is a tough job.
Even when successful, you drag home on Saturday night tired and dirty and battle-scarred. You know. How middle school teachers and peace officers and social workers feel every night.
Thankless jobs, and the burnout rate is high. Big 12 defensive coordinators are paid too well to burn out. If they're so inclined, their wives would tell them, burn yourself back in and go to work. But those salaries mean much is expected, and those coordinators are replaced on a regular basis.
Such as Glenn Spencer, whose defenses ranged from really good to just OK, including the latter in 2017, when OSU was a disappointing 10-3.