What is he going to sue them for, his own breach of contract? Saying that he should sue BYU is as ridiculous as saying someone who signs up for the military should be able to sue the military if they are dishonorably discharged for a violation of military rules.
Just because the signer of a contract doesn’t have the integrity to fulfill his obligations does not mean that the other party is equally bound to dishonor the contract.
If BYJ accepts Federal money, they might not have it that easy.