Globetrotters = Notre Dame, Michigan, Ohio State, Alabama, Texas, and currently Georgia (this list isn’t fully set in stone) these school can pull 3 million viewers playing Rice, UNLV, WKU, and the like even in an uncompetitive game.
The next level is still really good (some would argue that it’s all the same tier) but the main difference here is that they don’t get the benefit of the doubt when playing the little sisters of the poor so they need someone with a pulse to pull 3 million: Oklahoma, Penn State, USC, LSU, Florida State, Clemson, and Florida.
You can do this for each level down, as we drop down to the next tier you need a better opponent to hit 3 million+.
Obviously this compounds when these top tier teams play each other, even more so when ranked, and same applies to lower tier teams as well when ranked they can move up or down this tier system based on rankings and also what game are available week to week.
Big exception to this is when something like Deion and Colorado come along and break all the rules.