Because the plan God has for each of our lives isn't always the same plan we have for ourselves, Grace. Sometimes, our deaths have more of an impact than our births. It can inspire people to do great things, even greater than they would have had the deaths not happened at all.
The death of these people might have changed the world, Grace, so we might have changed the world, Grace, so we sometimes have to look at death not as something sad, but as something to be glad for. Sometimes death changes our lives in ways we never expect. It can bring with it every emotion; we have to learn to recognize the ones that help us and the ones that hurt us. And we also have to be willing to accept that with everything else, death also brings with it love. That is why we must always be grateful and appreciate it, even if it brings some sadness with it.