It's certainly not athletic directors or football coaches who make these decisions.
It's university presidents and boards of directors trying to increase revenue.
TV revenue from football and other sports is actually a lesser consideration compared to grants for scientific research, at least for the Big Ten schools.
That's why they'll definitely be interested in schools like Washington and Stanford to join their academic alliance too.
Ohio State's research expenditures recently surpassed a billion dollars a year, and they're only #24 in research spending across the country:
https://ncses.nsf.gov/pubs/nsf22311
The university presidents might've been more excited about adding UCLA than USC, given that UCLA gets more research money than Ivy league schools like Harvard and Yale. (Yet a sports-based conference also needs to consider the competitiveness of their teams.)
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