Not popularity, not football “prowess”, simply the value of the team to the media.
I have no problem with this list – I think they got it right – divided into 4 tiers in the video linked below. (In bold and italicized to represent tiers below.)
The first 2 teams are way above the rest in associated media value.
The last 4 teams are the ones I would expect to eventually be dropped from the B1G.
1 tOSU
2 Michigan
3 USC
4 Penn State
5 Oregon
6 Nebraska
7 Michigan State
8 Iowa
9 Wisconsin
10 Washington
11 UCLA
12 Minnesota
13 Illinois
14 Indiana
15 Maryland
16 Purdue
17 Northwestern
18 Rutgers
https://youtu.be/E0RDHWum-Js