Total speculation, but I think a thing Mack does is identify multiple power pivots of a program, whether it be administration or significant donors, and form deep, lifelong friendships with them. I think he's very good at that, especially one on one. I'm not saying those friendships are all disingenuous, but he does tend to barricade himself inside loyal power brokers. I think he's very tactical and focused on buying himself longevity. Before someone inside a program can even entertain a change in coaching direction, they have to weave their way through his loyalty armor. Honestly, I believe a lot of people do this, in any occupation, just as a self preservation bubble. But I think there are few people as good or better at that than Mack Brown.
It'd be interesting to hear from someone in the UNC realm who knows the ins and outs of their decision hierarchy. I'd wager that Mack has long, late night phone calls with several of them where he tells them everything he's learned they like to hear about themselves.