BYU football were lucky during the great times the honor code was not as strictly enforced as it is now.
The student body make up seems to be different also. A lot more nerdy. Some kids rightly or wrongly have that perception and just don't want to be in that kind of culture.
Just to be clear I don't use nerdy as a put down. Who wouldn't be thrilled with a kid or grandkid who get's straight A's. Prays every night on their own and has a goal of being a successful...................