(We'll say BYU is the boy in this scenario)
They don't understand it because BYU was still leaving something for nothing. Which was saying, to them, that BYU was better off alone than being with them. This is in part because of the comparisons to the other religious independent (**cough cough** Notre Dame **cough cough**) and the apparent belief that BYU must think they are as big a deal for going independent and following that model.
You're right - they don't understand.
I'm telling you what they DO understand. And if you want to know why they feel so angry about things, that is why.