The problem that Notre Dame has is that so many of the ED applicants come from the same socio-economic background, i.e. white Catholics from Chicago and Northern Indiana. If you are an active Catholic from that region, Notre Dame is more often than not the number one choice for college. I hear recurring stories how ND rejected the valedictorian of some south side or west suburban Catholic high school.
Unfortunately for that group, ND wants to be a national university, and can’t take the bulk of it’s class from a narrow demographic. For these kids, a rejection instead of a more polite deferral probably convinces them that they need to look elsewhere and not get hung up waiting on something that will not happen.