Humans like having the comfort of the illusion of predictability. It makes them feel like they are in control.
Death is an uncertain certainty, it can happen at any moment. You're certain its going to happen, however, you don't know when. We don't like that so we avoid it. We are happy clinging to the illusion of control, which is humorous because nobody has had any control since the moment of their birth.
We avoid death because death reminds us that we are not in control.
Just about everybody doesn't realize that the avoidance of death is the avoidance of life.
BTW - when I speak of death I don't mean demise.