It makes sense if you believe other people exist in a meaningful way similar to your own conscious existence. When you die, the universe doesn't cease to exist

It makes sense if you believe other people exist in a meaningful way similar to your own conscious existence. When you die, the universe doesn't cease to exist for them. So you are not leaving things behind for your own benefit. It's for other people. Conversely, if you believe the universe ceases to exist entirely when you die, you believe other people cease to exist too. In this case, perhaps the only consistent way to think of other people is that they are not like you when you are alive either. From a more down to Earth perspective, if I left the planet on a one-way interstellar FTL journey, confident I would never return and that there was no way to communicate with the people I left behind, even though it would be a relief in some ways and I'd stop caring about people left behind, I'd still want to arrange good things for some of them after my departure. Because I'm nice like that.