Why has my son been rejected by all Ivy schools

To put it as gently as possible, those are not the most outstanding stats, and plenty of kids with outstanding stats get rejected from Ivies every year. I do hope he has applied to some safety/match schools? None of the schools you have listed should ever be considered a sure thing.

(signed, parent of a kid with much worse stats than this, so congrats to your son for his hard work!)