Many animals end their significance in their species when they are physically damaged or when they get older. Commonly, they become an easy prey for other animals.
If we also had lives which end before the physical death, who would tell us about it?
The human mind cannot conceive the end of the individual to which it belongs, even if there is just a short time before his death. Surely, it could not make the man to recognize that he is socially dead.
Moreover, all those who could announce us that we are almost dead would hide such information from us. Instead, they could find in that secret many opportunities for themselves, from the egoistical ways of using what we still possess to the false and superficial feelings of compassion to some persons who cannot denounce the hypocrisy because they are dead. Many philanthropists make from this a real profession, striving for helping especially those people who could not have the right to speak or comment about the help they receive.
Besides, we often learn from our families to use what we find at our parents who are perceived by us as being dead for our future life.
Like many carnivore animals, the humans know that a living flesh is tastier than a dead one.