It's because the wide receivers are not that quick. They are fast but it takes them more time to make a move and get open. Watch the receivers on Oregon. They get off the line much faster than BYU receivers, make a quick move which frees up space. The half second makes all the difference. BYU usually has tall receivers with good hands. It fits their system and the quicker athletes tend to migrate to other schools. It has always been that way.