have been thinking about this - I think we are only viewing ratings as transitive, meaning we believe that if FSU changed conferences, their current ACC television ratings would stay the same no matter where they went. A different way to think about it, is that if FSU was matched up weekly with more competitive teams/larger brand teams, their ratings would increase because the matchups would be more enticing.
Team 1 has X fans
Team 2 has Y fans
Viewership of their game isn’t just X+Y,
it’s X+Y+Z (Z being neutral fans intrigued by the matchup)
In the case of ACC vs SEC/Big 10, it’s certain that the Z variable of potential viewers in those conferences is much higher than in the ACC.