the B1G is already making $55 MILLION per team... this move will move the SEC into the $60 MILLION per team. You're right, the B1G won't have to do anything, but they still could.
The ACC is only making $34 MILLION per team and the PAC is making $32 MILLION per team. If the ACC and B1G does nothing... the PAC will take Texas Tech, Oklahoma St, Kansas and KState... it will absolutely happen. That will get the PAC into Texas, Oklahoma and Kansas and WILL increase their revenue.
the ACC will most likely make a strong move to secure ND... if they can get ND, adding Iowa State is a value add to their conference as well
The remaining BIGXII teams are not sticking around to add BYU and some AAC teams and hope it makes a difference.