Earlier quoted context omitted.
Wait, so normally such patients are transported? For what? Billing purposes?
I've been thru EMT training. It boils down to EMTs not having formal medical education necessary to make a call as significant as pronouncing someone deceased. It's a blanket rule, so even in extreme circumstances like if you find someone beheaded, you just log it as a severe injury and transport the body to the hospital where a doctor pronounces them dead.
States have more and less sane approaches to this. Obviously, many things are not as clear-cut as beheading. But there are states that allow EMTs to make a field declaration, depending on specific guidelines, and possibly with the requirement of contacting a doctor to describe the situation and get their permission to terminate resuscitation efforts.