Because atpresent, there is a practical reality when the situation arises, one in which a specialist transplant nurse will look at who is present around the bed, and then quietly speak to the family member or members who they believe will best represent the wishes of the deceased.
But it manifests itself as a pure explosion of now: it catches us in its mobile, flashing present, which is the living reality it conjures on the page at the moment we are reading.