Who said that longevity should be a desirable goal? Aren't "brave heroes" the people that die for a "noble" cause? Isn't it villains that are more commonly depicted as ones seeking eternal life?
Is it better to go out in the prime of life, charging into the thick of things, living life fully than as a drooling, scared, physically weak old person with dementia? As with most things, it probably comes down to a middle point. Don't hide in a cave in fear of dying your entire life and don't give way to reckless abandon.
Old age comes with many ills. Both physical and mental weakness eventually afflict the old human. And to many humans, life on earth is a tough existence and a release from that struggle would be welcome.
Death is inevitable so what is the point of trying to escape it? Why go above and beyond to try and maintain a breathing body if the particular human is barely alive? It might be reasonable to patch a wound, but it may not be reasonable to go to extreme measures to heal the extremely sick. It is typically not for the sake of the extremely sick since it only makes them suffer longer. It is more to fulfill the emotional needs of those around them. This could be seen as cruel and selfish. Make the sick person suffer longer so that you can fulfill a need in yourself.
Death is not a "bad" thing. It is as much a part of us as birth. You can't run from it, and doing so has caused a lot of suffering. Humans think of death as something that causes them to "lose" their loved ones. Mental illness, long-term-kidnapping, long-term-arguments, and ending of relationships can do that too. Is death all that special, should it get such a negative stigma? At least with death, there is at least one person not crying, feeling sad, or suffering.
It is immature for humans to try and cling onto "life". Keep yourself healthy and tend to your wounds. Let the extremely sick live out their lives in comfort without prolonging their suffering and without extreme measures. Learn to deal with loss since it could come from other places besides death and it will be something you have to deal with eventually anyway.