I understand the technical reason, but from the point of view of player safety, why doesn't 15 minutes count as 30 seconds.
From my perspective, it's as simple as this - it's not punitive.
Yes, the helmet rule is about player safety. However, forcing a player to sit out the subsequent play after losing his helmet is not for the safety of the player. The intent is to make it 'expensive' to wear your helmet in such a way that it comes off too easily in the heat of battle.
The rule is more of a teaching tool, if you will, and it has already reduced the number of lost helmets I've seen in my games over the last year. It will continue to trend that way as long as the rule makes it 'expensive' enough. If in a tight game a coach has to choose between losing his QB or a valuable TO, he would rather staple the helmet on his kid's head instead of being faced with such a situation.
Who knows, it might even return to the way it was in my playing days where it almost took emergency equipment to remove your helmet on the sideline and the resulting 'helmet head' imprint was with you for hours.