Your understanding of UGA football is not accurate.
Richt replaced Jim Donnan as the HC at UGA.
Donnan was 10-2, 9-3, 8-4, and 8-4 is his last 4 seasons at UGA. They fired him because they believed they were better than that ... They believed, then, that they should be a perennial contender.
Richt making them a perennial contender didn't change their expectation ... He met the expectation. And he was fired when they decided his best days were in the past, and couldn't keep them as a contender.
Miss St. was never going to fire Mullen for going 8-4 every year ... BECAUSE THE PROGRAM EXPECTATIONS ARE DIFFERENT.