The most noble, selfless reason I could think of is "so that they try again". I say, the "most noble" because people have plenty of more selfish reasons: "they'll make me feel better", "to make me a better person", "to keep up with the expectations of my friends and family", "they'll give me comfort when I'm old and frail", "they will care for me". And then no-reasons such as "it's the way things are", and "everybody does it", and "god wants it".
But I prefer mine: "so that they try again". Try what? To right the wrongs, to succeed where we failed. But that is a mirror: if my kids inherit the world of my failures, can I look back into my soul and say that I tried hard enough? When the day they lose something precious comes, and they understand this world is mostly darkness, will I be able to look them in the eyes and say that I tried hard enough to beget the light they crave?