The pope can reject an ambassador because the ambassador is sent to HIM. The pope is less likely to deal with a problem in America because that is left to the American bishops. He might do something, but it is doubtful. This is a problem for Catholics in America. We should be able to solve it on our own. That’s the principle of subsidiarity and the pope believes in it strongly.
Americans SHOULD be able to find a solution but Notre Dame has such an important image among US Catholics and society in general that some special attention seems warranted.