Blood Oxygen for Minors (Series 6)

Why can't this be used for consumers under 18 years of age? Is it because their bodies are still developing and therefore susceptible to seemingly random fluctuations that could otherwise be classified as severe medical conditions?

Is it because minors are not legal adults and it may be held liable to Apple?

I am just curious since it defeats the purpose of buying a 6 rather than a 4 or 5.