It has all to do with the numbers of 5 star players who want to be challenged academically. It is a very small percentage and Stanford, Northwestern, Vandy, Rice, Virginia, and Duke want those two or three also...and some years there are not any. It is pretty simple. Other schools at which those players can get a top and challenging education actually try to steer great student athletes onto an easier path.
ND is in of a few five star players every year, but getting them to give up the easy path is not in the character of most of them.