Short answer: your question sucks.
Long answer:
Humans have this ability to imagine themselves in someone else's shoes. It's arguably one of our most important traits.
Your question seems disingenuous to me. Are you honestly saying you can't possibly imagine why someone might fear death? I don't believe in any sort of an afterlife, and the thought of my own death just gets a "meh" out of me, but I don't think it takes that much work to come up with a couple of situations where you might be afraid of death. For example, you are a religious person, you believe that if you do certain things you will be rewarded after death, and if you do some others you will be punished. You hope your "good" column is longer than your "bad," but there's really no way to tell until you're dead, and by then it might be too late. Or you have some loved ones who depend on you for support, and you are afraid that if you die they will not be able to take care of themselves well. Or you believe you have a certain mission in life and you fear that if you die you won't be able to accomplish it. See? Not that hard.
You don't seem to like some of the answers people have given for why they fear death, which makes me think you're fishing for someone to either change your mind, or to have the poor death-fearing-schlubs be awed by your epiphany that "death is inevitable" and change theirs. Most people are already well-aware that death is inevitable, and in fact, it being something you can't escape probably contributes to, not detracts from, their fear of it. You're asking people to tell you highly subjective and personal reasons, and then arguing with them when their answers aren't good enough--like asking what everyone's favorite color is because you're "just trying to figure out" what colors people like, then telling them they're wrong when their taste doesn't exactly line up with yours.
In your first response to Kat, you start narrowing down the definition of "death" (for this conversation) to a ridiculous point. You say it's ok to fear the "before and after," but you don't understand why fear "death itself." When people speak of death they're not just speaking of the millisecond when they stop breathing (or whatever other measure they're using to gauge life vs. death)--they're speaking of the time and events
leading up to death and what might come after. Again, I find it really hard to believe that this never occurred to you.
You also say "Why make an 'event' so depressing?" Are you kidding me? Humans imbue events with meaning and build emotions around them. It's what we do. We celebrate birthdays, religious holidays, sports, get depressed about stuff that happens to our friends, at work, when our favorite toy breaks, whatever. Death is by no means the only place where we make an "event" depressing/happy/takeyourpick.
If you honestly can't imagine where people are coming from on this and you're an adult, you have issues. Big ones.