Because we think in stories, the final moments of a life have outsize importance. If a woman has 99 years of misery and privation but is vindicated and honored in the hundredth year, we think of that as a good life. Yet if a man has joy and honor for 99 years but dies alone and neglected we find this terribly sad. Daniel Kahneman wisely notes that because memories are the part we can take with us, we overvalue the end of the story. "If you want good memories, all you need are happy endings."
I see that this is quite crazy, of course. The 99 years have 99 times the value of the one. Yet as a person who lives in memory I absolutely get it. Memory is the part we get to keep. We have a drive to tie up the lose ends, to tuck a story into bed so that we can let it rest forever. Stories that are still up and walking around make us nervous.
Relatedly (Kahneman again), because we strive to maximise satisfaction with ourselves rather than happiness, we push consistently pleasurable activities like spending time with friends to the back of the line.