First, there aren't very many each year. You've got about 30 or less to work with.
Second, of those 30, how many are academic fits to Notre Dame? That cuts the list by a good amount I imagine, so let's say 20.
Third, how many are interested? Half of that? So let's call it 10.
So it's about 10 each year with some interest, give or take, who may or may not want to go to a school in a cold climate, where you won't skate academically, can't focus solely on football, and isn't the most fun place socially. For some, the positives outweigh the negatives. For most, it doesn't.
Notre Dame has to get lucky with fit, geography, and interest. They did this year with Tyree and Johnson.