The RPO craze at all levels of hs football has forced defensive coaches to use more man coverage concepts, thus the DB's have to play tighter coverage and less eyes on the ball. Old school zone allows OC's to put defenders in conflict and hit the RPO's. Man coverage employed by DC's get the defender out of conflict. And because most RPO's are of the quick pass variety, DB's are forced to hunt up the receivers immediately, reducing vision on the ball