All the icky crap comes from knowing that can't be.
The subconscious dread of death is also a form of the Fear of Missing Out. How much cool tech and new discoveries will there be after us? I for one cannot cope with the possibility that I may never get to see a proper ending to Game of Thrones or a good Dungeons & Dragons movie.
This is a strong universal claim about a fact, and I'm pretty sure that it is not true. While probably generally true for young people, research on older people suggest that not everyone wishes to be immortal and some are actually in peace with the approaching end of their life.
Just one result from a quick search: https://journals.plos.org/plosone/article?id=info:doi/10.137...
Exactly, by very definition of getting "older", they already know it's damn well not going to happen. They feel their frailty and corporeal limitations, and have lost other people to mortality, so they learn to cope with it, via the very topic of this post: Terror management or whatever you want to call it.
I said at the core, because the purpose of any mind is to, well, mind. If a mind wishes to cease to exist, it's because it's unable to attain its desires and knows it will never have enough time (for some, to even find a desire in the first place.)
I've always been fairly morbid myself. If given a choice, I'd choose to be immortal or never have come into existence at all, rather than this temporal teaser.
Like the comment below by rinchik [0], our global culture encourages every mind to .. succumb. We're discouraged from feeling, from the core essence of sentient existence.
That is true. I've been thinking about death more in the recent years, and most recently, the thinking focused on ideas like "if there's no afterlife, I wish there was at least a 'high score' screen, and a way to see how did the rest of humanity fare, how life looks a hundred thousand years from now".