I don't know why so many humans long to live forever but I have always wondered if it was the price we paid for evolving into self-aware humans.
I agree that animals also fear death when they are threatened, but it is kind of hard to know if they fear natural death because they wonder if they have been "good enough" little critters to make it into Jehoho's paradise. Fear of destruction or hell or anything else fantasized as unpleasant puts a whole new twist onto the fear factor.
Lots of things in life are hard to accept, but death probably is the hardest. I have heard though, that the closer you get to your own death (by aging naturally), the more you accept it and become more at peace with it. Who knows if that is because they believe they are going off to somewhere better, like heaven or paradise, or wherever.
If you logically think about it, though, our bodies were not made to live forever. There is not one biological thing that exists that lasts forever and never dies. So, either death has always been a natural occurrence of the human species, or when "Adam and Eve sinned" in the Garden of Eden, Jehovah decided to impose death on all living creatures in the Universe instead of just humans, but really doesn't make any sense ... for any fairy tale.