One thing to remember, at the HS level around here, no QB is finding wide open guys immediately, they each have a predetermined guy they're throwing to when the ball is snapped.
What makes the difference between a successful passing attack or not, is what comes next with coverage, pass rush and QB.
Is the predetermined guy covered, is the QB pressured, can the QB run?
If he has time he "might" actually find an open receiver. However, most of the time one of 3 things happen, the QB throws it anyway, he takes off running, or he throws it away, the least likely option.
If coaches consistently see an open guy, then they call that guy to get the ball until it's stopped.