I mean the answer to this is easy... it's about exposure self-selected by networks.. and lack of other options, particularly in the early portion of the timeframe. I mean if you accept Tony Altimore's data Florida, Clemson & Auburn are all more effective than Florida State in driving viewers over the last 8 years. That's something that I would be skeptical of, as Florida or Auburn could be replaced with generic SEC team vs Georgia or Alabama and draw similar ratings; Clemson's viewership is boosted heavily by its 10 playoff games during that window, recent seasons have shown the massive decline as they stopped being relevant; while Florida State's brand still has the power to make an otherwise unairable matchup with Wake, have some value to be aired.
So while I have no doubt that the data is accurate, it's a bit of a self-fulfilling prophecy. The networks put the teams they've always leaned on into time-slots that have historically strong ratings on networks with broad coverage; unsurprisingly those games draw higher ratings. I would hazard a guess that you could swap out the bottom third of that list for generic state school having a good year and it wouldn't move the ratings much, those ratings aren't coming from who the team is, but what network the game is on and what other options were available; its ease of access as much as anything.
The data is also from Nielsen counted games from 2016-2023... so it's got the end of the cable era (hell even ESPN+ hadn't launched yet for the first two seasons); an era where TV viewership and valuation is much different than it is now. The data is also an aggregate which means the bottom 71% of programs had only a fraction of their games on Neilsen counted networks; the lower exposure essentially forces them into the bottom spots (again that also goes back to a history where they've been unproven as draws, resulting in a lack of opportunity). That 71% now has greater exposure, but that exposure comes on streaming services (not Nielsen rated). The end result of the greater quantity of options on TV has been that ratings for the "prime" broadcast windows have declined. It is my belief that the real value over the new landscape will be those programs who have the brand-value to drive subscriptions over eyeballs.
To that end, it's been proven over the years that dominant teams (and brands) tend to draw ratings. The Patriots & Clemson drew monster national ratings when they were relevant. Now that both teams have tailed off a bit, they are no longer the ratings powerhouses. Clemson has value as a perennial 11-1/12-0 ACC championship team, even if their conference is not considered elite; it has much less value as an 8-4 team in the ACC or any other conference (similar to how Florida's value in that data comes from the SEC brand, not the Gator brand). That has to be priced into any move from a network value perspective, when you have consolidation you are going to reduce the number of those "dominant" type of teams and records, which ultimately reduces the inventory of games that are attractive to casual fans/advertisers; unless you can convince the fan-base that inherently not because of the teams, but because of the league, the game is important. That is what ESPN has been doing with the SEC.. trying to convince fans that because its an SEC game, Mississippi State - Arkansas is an important matchup worth watching. In a world where more content has to be sought out, it's going to be a tougher argument to make.. and they risk losing bandwagon fans (which are still a portion) if formerly dominant/readily airable teams move to a new conference and become middle of the pack (think Nebraska going from a program with dominant value (similar to Clemson in Altimore's data) to just another midwestern school in the Big Ten).
TLDR: There's no question as to why they scored more viewers.... they had greater opportunity on Nielsen rated networks with higher carriage in better time-slots for 8 years starting in an era that no-longer truly exists, that doesn't necessarily mean that those 18 programs would continue to be able to maintain similar ratings in a world where the P2 separates.
