Pitch calling is, in essence, a coaching strategy. Strategy is the domain of the coach in high school baseball. I have always held the position that a catcher learns quite a lot about the game by paying attention to how a coach calls a game. A good coach will discuss his game plan with his battery and share his expertise. They can benefit without calling the game themselves. There have been times I let the catcher/pitcher call the game, but those were learning moments - not to learn how to call a game, but to learn to pay attention to overall strategy.
Now, in the majors, where catchers have extensive scouting reports and often have seen the same batters hundreds of times, they are, in effect, coaches on the field and are armed with what they need to call a game. In high school, they simply aren't. When the time comes, if they've had the benefit of a good high school/college coach and paid attention to how he calls a game, they'll be ready.