The Big Ten pays out more annually to it's members than the SEC. So the financial hurdles in adding schools to the Big Ten are higher than in the SEC. (This will change once the CBS SEC game of the week moves in 2023. But until then, the Big Ten's revenues will exceed the SEC).
The only school that moves the needle for the Big Ten or SEC is Notre Dame. And ND isn't going anywhere until 2036 at the earliest (unless they join the ACC, which they can do anytime until 2036.).
The Big Ten's TV Deal expires in 2024.
And now here's the big thing.
ESPN/ABC now has control of the entire SEC portfolio for football, and pretty much took all the value from the Big 12 with Texas/OU. ESPN/ABC will have the 12 team College Playoff. And until 2036, ESPN has the ACC.
So now there's going to be CBS, Fox, Turner, and NBC all bidding for Big Ten rights along with ESPN. The Big Ten is going to want to get paid, so here's how it goes below.
1. USC/Oregon sees the Pac-12 falling apart and all the Big 12 leftovers are out too.
2. The big thing about the "ACC rights are good through 2036" is actually bad if Clemson/FSU look and see the SEC & Big Ten are getting massive amounts more money than this ACC
3. The Big Ten is the only conference that can compete with the SEC and has a good structure in place. So they will be adding 2 or 4 new programs guaranteed.
4. The needle moving may be true for the SEC, as their games just get viewers and ND would be the brand that gets them into the Midwest and Northeast, heck nationally, ND has a national fan base. But, the Big Ten would stand to gain a lot more to get into places like the southeast and add ND's market. They added Maryland and Rutgers to try to get in the northeast, but ND would guarantee that audience.
The new SEC & new Big Ten super conferences will put them on a level where their TV contracts will be insane amounts. If some programs want to leave, then the new TV deal or conference will have enough money to buyout any agreement. Money to leave or some contract isn't going to hold them.
The ACC has to get BOLD.