Not sure if you understand my point. My point was that being independent was rather common before 1990. But for years prior to that, the NCAA limited the exposure of each team on TV either nationally or regionally. Georgia and Oklahoma sued to own their own TV rights and won in the Supreme Court in 1984. This started negotiations with networks and schools and conferences. It was clear that the networks wanted to limit the number of negotiating partners, so that's why the Big East added football and picked up Miami (but refused Penn State by a 5-3 vote championed by Pitt) and then negotiated a TV contract. Paterno was pissed and that is why the annual game between PSU and Pitt ended, and then PSU went to the big ten.
The real genesis of all of this was the creation of an organization called the College Football Association (formed in 1977) to help independent schools (such as ND) and some conferences to get TV contracts. Not all schools were members, but the NCAA threatened sanctions against any school working with the CFA. That led to the lawsuit that the NCAA lost.
When ND got its NBC deal in 1991, it left the CFA. But no other single school could replicate that NBC deal and many independents started looking for a conference home. And as college football grew in the 1990's, conference "realignment" began as the conference led TV contracts became more valuable....and more negotiable by changing members. The CFA disbanded in 1997 as it no longer had any purpose.
Without the CFA, ND would have to negotiate its own TV contracts or join a conference. It basically did both. As we all know, it joined the Big East - and then the ACC - for all non football sports. And it kept its football independence with NBC. But unless ND can keep its NBC contract, or replace with another network, it would have to join a conference to get any TV revenue for its football games.
It is my understanding that NBC did not have a lot of competitors for the latest renewal. I am not sure if $15M per year is the correct number. ND got $8M from the ACC and about $3M from the college football playoffs (they get that whether they are in it or not). The ACC gets $66M a year from the playoffs to be shared by the 14 members. FSU got $28M from the ACC last year; Clemson got $34M. Each SEC school got about $10M-$15m more than that, per member. The Big Ten gets the most per member.
Money doesn't matter until it does.