There's a huge difference between what Briles is KNOWN to have done and what Mullen MAY have done. Mullen may have known Zach Smith was a POS, he may have known that Hernandez was trash, but ultimately, it was Meyer who ran the program and it was him that made the personnel and staff decisions. The head man sets the tone and as we've seen with Briles and his apologist son, the tone is one of "I want to win and if it means some random coeds get raped ,then so be it". There's a reason why no one worth a **** wants Art Briles around.
Mullen as a HC didn't stand for that, and if you look at how he disciplined at Mississippi State and Florida, he showed that he was willing to at least try to run a program that didn't put up with trash behavior. There's a reason why Mullen has a future in coaching, while Briles is coaching HS ball at random stops, and when someone tried to hire him at the collegiate level, the backlash was so incredibly toxic, Hue Jackson had no choice but to back down. Again, why should Miami deal with that, when there are DOZENS of OCs worth a **** that Miami could hire?