Exactly. So why worry over it? Why be depressed over something you have no control over? Worshiping an invisible being that we conjure up in our minds won't change that.
I think it would be because some people just want to live forever and find the greatest value in living forever. We are hardwired for survival after all. Living forever gives them and their human forms a sense of greatness in their own lives. Immortality is a compliment to these types of people and is like saying to them: "Since you are a great innocent person, then your human form and your life should also reflect that said greatness. In other words, just because you are a great person, then you deserve something of the greatest value which would be immortality. If you find immense value in this life you are living now, then you would obviously find the greatest value in living in that said life forever and even living on in an afterlife forever. This life is meant for all good innocent people which means that all good innocent people should get what they want as long as it is something that doesn't harm and demean others. For me to tell you that your human form will just rot out in the end like a rotting piece of meat would be offensive to you since it is like saying to you that you have this great innocent personality, but your human form is pathetic and inferior and doesn't adhere to that said great personality of yours. It is like saying you are not worthy of that immortal life which would be the life of greatest value to you."
But for an atheist who finds immense value in this one and only life, then it is different. So it's all just a matter of different people having different tastes in life. Some people value living on forever as the greatest life and they would never go bored or insane from such a life while others would go bored and insane from such a life. It all just depends on your preferences.
But as I said before with the implicit atheists, they already do have a sense of living on forever and find the greatest value in that said life since if you are unaware of death, then the only thing you are aware of is living on forever. The same thing applies to animals in that they are aware of nothing but living on which means that they are aware of nothing but living on forever and they find the greatest value in that life.