Not using players as much until they know the system isn’t a Frank Reich thing. It’s what most coaches do.
Young players who don’t know the system make more mental mistakes. Much more. Coaches try not to overwhelm young players by giving them too much too soon. Players earn more time and trust by succeeding with a smaller sample size.
Young players who are playing a lot are more the exception than the rule. But you read more about them, they’re the success stories. But the vast majority of rooks start small and work their way into more.