To the extent that you have a choice in the matter, the reason not to fear it is because feeling that fear all the time is going to be a miserable existence that will likely drive you to an earlier grave. That said another way your question could be interpreted is, “why wouldn’t death be considered scary?”, which is that’s your meaning, it is scary, it’s probably quite literally the scariest thing given how strong survival instincts are and the role that fear plays in those instincts. The reason people are not generally always in paralysing fear is because that fear that in some situations keeps them alive, ceases to be useful for most of the rest of one’s life and is actively detrimental to the very survival it’s supposed to safeguard. However, the fact that most of us are not unduly preoccupied with a great of death is probably less to do with an active decision or rational choice and just a healthy instinct to steer our thoughts away from that cliff once thoughts drift too far that way and we experience unpleasant emotions. As far as we know, we’re the only species on the planet that deals with the knowledge of our own mortality so the extent to which this affects your daily probably has some greater degree of conscious mental decisions so I guess that’s what makes it possible for a person to get fixated on the issue and develop unhealthy patterns of thought around it, that might be what’s going on for you, but the other side of that coin is that that means it’s at least somewhat within your power to reach a comfortable medium point between acceptance of mortality and a healthy amount of attention and thought towards it.