Obviously it starts with recruiting, and then player development, and then scheme, and then gameday, and a few other items (conditioning). Everyone knows that.
To the extent 247 recruiting figures means anything, Tenn has ranked 17th, 21st, 13th, and 10th since 2017. UGA has ranked 3,1,2,1 over that period. That is a difference in getting several five stars versus one, or none, plus 4s. When you recruit 5 stars, many can play as freshmen, and get experience, so when they turn over a year they are quite good (often). A three star obviously can become elite, but usually it takes time.
When your second team defense is basically as good as your first, and both are very good, you just keep pressuring and playing at a high level, no plays off. When Tennessee is consistently in the top five in recruiting, they will equalize on the basic talent level and be "back".