You're ignoring that they actually want Kansas. They really are a school that Big Ten presidents like and think would fit perfectly. True, they don't "have" to go to 18 if they get Oklahoma and Texas... but they actually want to. They like the scheduling 'symmetry' it creates, from everything I've heard. Plus, if the Big 12 is eaten alive, we will wind up with four super conferences anyhow and it would essentially create an 8-team playoff. At that point, they'll create a third subdivision or else the rest of FBS would be absorbed into FCS.
Would love some non Non-Key Tweet sources on this.