The game clock stopping on first downs is simply a rule that hasn’t been changed at the high school level because the rules committee hasn’t deemed it necessary like NCAA (under pressure from its conferences’ TV partners) has. And assuming NFHS still wanted the clock to stop inside two minutes like NCAA, now you are creating another exception and we all know NFHS tries to avoid exceptions.
We can hate on NCAA rules (and NFHS rules makers nonsensically make trickle-down rules more complicated than they need to be) in this forum all we want, but let’s not kid ourselves – the :40 play clock was passed because more high school teams are now running college-style offenses, and requiring a ready-for-play whistle subject to every HS referee’s individual pace was no longer fair or feasible. It’s bad enough when HS crews have overweight officials who struggle to get into position efficiently, and not letting A snap the ball on the ground because of a slow down box completely eliminates why the change was made. The NFHS mechanics POE supports this.