Sadly it's not really a head scratcher, many of those kids aren't Catholic and could care less about the ND Degree. They go to Catholic schools because that's where best football is in Chicago.
But for many of the top recruits its about football, fun and sex. If you don't care that much about school then ND is going to be a hard sell no matter how good the program is doing. They can go elsewhere football is king, school is secondary and a University has an abundance of fun and an abundance of girls. That is something that ND can't offer.